Every touring pro is both skilled and strong -- an artist, expert in shot-making and movement, and also a thunderer, able to draw on severe power. Even as points and matches are sometimes won by the artist's tactics and variation, in today's game to play softly, i.e., unforcefully, usually allows fatal dominance to the opponent. Thus all pros are both artist and thunderer, where only the proportions in mixing the two vary.
 
Not too many years ago there were two distinct populations of pros. There were the clay-court "specialists," who generally stayed in back court, happy to engage in extended rallies, skilled in delivering topspin, practitioners of drop-shots and other variations, inclined to play defensively. Players raised in Spain and South America epitomized this group. Then there was the second population -- the fast-court warriors, generally reliant on very potent serves and forceful ground strokes, often attacking net to end points quickly.
 
Today the two populations are less well defined including at topmost levels, where most players are almost equally able in either clay or fast-court realms. Still, the old picture is not entirely gone, as service aces remain fewer on clay than on hard courts, and breaks of serve more frequent. The slower bounce on clay surfaces still favors the defensive-minded player, even as aggressive hitting with attending risk of error, on clay offers less likelihood of hurting opponent.
 
Generalizing loosely, we can view clay specialists as the "artists" of the game -- players primarily adept at variety, placement, court movement, spins, and avoidance of error. The hard-court warriors, in contrast, are then the "thunderers," largely reliant on power in serving and stroking.
 
But recent successes of the tall and powerful American John Isner in Davis Cup action on clay seem to upset entirely the old paradigm. John's first serve is so strong that it loses little effectiveness on clay, and his overspun second serve is almost equally dangerous because of its weighty and extremely high bounce. Isner is also capable of extreme power in stroking with seemingly easy effort, especially in the forehand, usually with good disguise. Thus if opponent manages to return John's serve but without plenty of mustard, John is ready to rip his own reply to a corner and move forward to net, where his volleying and overhead skills are excellent, indeed superior. It is hard-court "first-strike tennis" in almost pure form but executed by John on clay, often brilliantly.
 
As the European clay season further unfolds, will more success on clay by Isner and by others also of thunderer bent -- Milos Raonic, for example -- foreshadow wider use of tactics where early and extremely heavy attacking is more widely seen as a way to win on clay?
 
Artists and thunderers are also delineated among the women. Representing the extremes are (1) the highly varied style of artist Francesca Schiavone, who captured the crown at Garros two years ago, and (2) the relentless thunder of Maria Sharapova, who at Stuttgart last week won the leading women's tournament to date of the European clay season.
 
CLAY-COURT ACTION 2012
 
This year's pro clay-court action began in February in Latin America. In the absence of the men's Big Four, Spanish stars David Ferrer and Nicolas Almagro collected the top laurels in the four-tournament circuit. Then April brought the U.S. Clays in Houston, won by Juan Monaco over a tired Isner, followed by the Masters-1,000 tournament in Monte Carlo, where Nadal defeated Djokovic in the final round. Meanwhile Serena Williams won the Family Circle Cup on clay in Charleston, and Sharapova won at Stuttgart. Several Davis Cup and Fed Cup early-round meetings produced other important results on clay.
 
But the greater clay-court action for 2012 lies just ahead, including prime tournaments for men and women in Rome and Madrid, with the main draw at Roland Garros to start on 27 May. Last year the men's Big Four -- Djokovic, Nadal, Federer, and Murray -- dominated these events, placing three members of the four in the semis at Rome, three at Madrid, and all four at Garros. Our survey of candidacies thus begins with them. (The stated odds, obtained by subjective judgment, represent the current outlook for any of the three events.)
 
THE BIG FOUR ON CLAY
 
Rafael Nadal (odds 2-1)
 
There is magnificent artistry and thunder in the tennis of Rafael Nadal. That Rafa has surpassed Bjorn Borg as history's greatest clay-courter seems clear. In an analysis here two years ago we placed Bjorn slightly ahead of Rafa, but since then Rafa has added two more Garros crowns, making six in all, matching Borg's total, and has surpassed Bjorn in total clay-court tournament triumphs.
 
Rafa turned 25 last year, when the year's overall champion, Novak Djokovic, nearly outscored Rafa on clay as well. Over the years, Rafa's brutally physical style of play had worn down opponents but also been hard on Rafa's own physique. Last year, still bothered by a hamstring problem incurred at Australian Open, Rafa lost to Djokovic in the final round at both Rome and Madrid 2011. Things looked even worse for Rafa when in the first round at Garros unseeded John Isner, attacking very effectively, won two tiebreak sets to force Rafa to five.
 
But after defeating Isner, Rafa went on to capture his sixth Garros crown, winning a four-set final against Federer (who had beaten Djokovic). Having also won Monte Carlo, where Djokovic did not compete, Rafa finished slightly ahead of second-place Nole in clay-court points earned in 2011.
 
The pattern reappeared in early 2012. A left-shoulder injury from 2011 troubled Rafa early in the new year, and a damaged knee forced Rafa's withdrawal from the hard-court event in Miami in March. Rafa seemed healthy at Monte Carlo, triumphing there for the eighth straight year and beating Djokovic convincingly in the final. A week later he added an eighth Barcelona crown.
 
Novak Djokovic (odds 2.5-1)
 
Slender and athletic at height 6-3 and soon to be age 25, and having won four of the last five Slams, losing only at Garros 2011, Novak's preeminence on nonclay surfaces seems complete. His is a game of moderately forcing but well-controlled pressure, administered on every shot, backed by superb court mobility. There is too in Nole a inner relentless determination to prevail -- seen in his knack for outlasting opponents in the many fierce and extended exchanges that his style seems to create. He is ready and able to end points quickly when opportunity arises, but his hallmark is in drawing out matters with relentless but relatively risk-free pressure.
 
Still in question is Nole's ability to defeat Nadal on clay. As pros the two have met on that surface twelve times over the years, Nadal winning the first nine. Nole then won their two clay meetings in 2011, at Rome and Madrid. But Rafa won their only 2012 clay meeting, at Monte Carlo, producing his best tennis while Nole seemed mentally burdened, probably by the recent loss of a grandfather.
 
Roger Federer (odds 10-1)
 
Roger at age 30 wields superior skills in all aspects of the game, along with knowledge from more than a decade of top-level competition of how to employ these skills. He may be history's greatest artist of the game even as he commands extreme thunder when needed.
 
Roger's prime opponents are five or six years younger than he and are certainly stronger in stamina. Roger, however, is skilled in rationing his energy in long and intense matches. Undoubtedly Roger will plan his spring campaign to prepare primarily for Garros, but he will nevertheless be a strong candidate at either Rome or Madrid, where matches are shorter (best-of-three sets vs. best-of-five at Garros) and where to win the crown seeded players must win only five matches (vs. seven at Garros).
 
Andy Murray (odds 30-1)
 
Murray's playing skills seem well suited to success on clay -- the easy power, the excellent movement, the defensive tendencies in his playing style. A good part of his early training was in Spain. But although Andy has won 22 tournaments in his pro career, he has never won a clay-court event. Moreover, as a pro he has never beaten another member of the present Big Four on clay, having lost four times to Nadal and twice to Djokovic on that surface.
 
His early exits at Monte Carlo and Barcelona show that Andy is the least likely of the Big Four to prevail in the coming big clay events. He could -- perhaps should -- reach the semis in any of them, but despite his fine assets his chances of going farther seem faint.
 
THE OTHERS
 
Most of those likely to threaten the Big Four are ranked within the world's current ten or fifteen. Several have a career edge on clay over Andy Murray -- i.e., Tomas Berdych, Juan Martin del Potro, Nicolas Almagro, and Juan Monaco. (Berdych recently beat Andy at Monte Carlo, and riser Milos Raonic defeated the Scot for the first time last week at Barcelona.) But although these contenders are able to extend and occasionally win a set against the other Big Four members, none appear capable of beating Djokovic, Nadal, or Federer by winning three of five sets at Garros or even, less surely, two of three on clay elsewhere.
 
--David Ferrer (odds 20-1). This Spanish veteran, height just 5-9, captured the clay tournaments in Buenos Aires and Acapulco earlier this year. David's determined play creates many highly watchable points and games, but he has lost his last nine clay-court matches against Nadal, including their closely-fought recent final at Barcelona. He holds a 2-1 W-L edge on clay against Djokovic, however, though he lost their most recent meeting on clay, at Madrid 2011.
 
--Tomas Berdych (odds 30-1). At age 26, height 6-5, and 200 pounds, Tomas brings good clay-court credentials, including a 62% career main-tour match-winning percentage on clay (vs. his overall 63%), following a preponderance of clay-court competition earlier.
 
--John Isner (odds 30-1). When John produces his best first-strike tennis, he is capable of dominating any opponent on any surface. Also, when exchanges become extended John is usually able to maintain neutrality, keeping opponent deep while staying ready to force play with well-directed extreme power. He uses the score to aid his strategy and is skilled in exploiting his serving prowess to reach, and then win, set-ending tiebreakers. His wins in 2012 clay-court Davis Cup play over Federer, Simon, and Tsonga (and a win over Djokovic on a hard court in Miami) commanded major attention.
 
--Juan Martin del Potro (odds 40-1). This strong Argentine player is both taller at 6-6 and younger (by three years) than Berdych. His early development and play were focused on clay, and his later career clay-court achievements have been auspicious, including a triumph at Estoril last year and an overall career clay-court winning percentage of 70%. His excellent power in serving and stroking mark him more the thunderer than artist.
 
--Jo-Wilfried Tsonga (odds 60-1) brings plenty of power, athleticism, and variety, but he has never beaten any Big Four member on clay.
 
--Nicolas Almagro (odds 75-1). A potent server and striker, Nicolas at age 26 was second to Ferrer as top point-gatherer at the 2012 Latin American clay swing. Nicolas has never defeated Nadal, Djokovic, or Federer in nine clay-court match-ups.
 
THE CURRENT POWER ROYALTY IN WOMEN'S TENNIS
 
Dominating the women's game at the moment are two superstars -- Victoria Azarenka and Maria Sharapova -- even as one of the few megastars in tennis history -- Serena Williams -- remains yet a threat to move toward her former place. The three together compose the current power royalty of the sport.
 
Victoria Azarenka (odds 3-1)
 
Victoria Azarenka captured the crowns at Sydney and Melbourne Park in January 2012, and she won her next two tournaments, at Doha and Indian Wells. Three more match wins extended her consecutive victories to 26 before the streak finally ended when Victoria, probably tired from her run, lost a straight-setter to Marion Bartoli in Miami. Then came the indoor clay-court tournament in Stuttgart, where Vika had trouble dominating Barthel before advancing impressively against the softer game of Radwanska. But in the final round, with her serve and forehand perhaps hampered by a weakened right wrist and facing a Sharapova at her best, Vika lost in two not-very-close sets.
 
Born in Belarus, Victoria lived and trained in Arizona for many years and now lists Monaco as her residence. At age 22 and strong at height 6-0, she is confident in knowing that there are no players outside our power royalty able to dominate her without severe risk of error -- that if Vika can find her best tennis, she is almost certain to prevail. Like Djokovic's current formula, Vika's is both relentlessly forceful and remarkably free of error.
 
Most of Victoria's successes have come on hard courts, including her streak of early 2012. Her clay-court record last year was unspectacular, showing a #5 ranking in clay-court points by my count, compared with her official rank of #3 on all surfaces. There have been no retirements from matches this year by Vika -- a vexation that came often in 2011 and before. If the bothersome wrist is fully healthy, Vika's rekindling on clay the improvement seen during the streak seems probable.
 
Maria Sharapova (odds 4-1)
 
At age 25 and height 6-2, Maria seems the pure thunderer -- wholly reliant for her success on extreme power in serving and stroking. During her career she has won each of the other three Slams, but she has never gone beyond the semis at Garros in nine tries. (She did win the Italian in 2011, however.) Her stroking power can penetrate even on slow clay, and her serving is fiercely aggressive.
 
At Stuttgart she defeated Stosur closely, then took advantage of many dismal errors by Kvitova in the semis. Against Azarenka in the final, Maria's rocketing first serve was at its best, her high toss unbothered indoors by wind. As earlier in the tournament, Maria's second serve was only slightly less forceful, carrying excellent depth in the service box. Unlike earlier, there were few double-faults by Maria, and also remarkably few errors in delivering her ground stroke screamers. She was better than Azarenka in attaining early and best hitting positions for her groundies.
 
The highly enclosed courts at Madrid should provide a good venue, largely free of wind, for Maria's strengths. Our calculations, based on weighted results of 2011 and 2012, confirm that Sharapova and Azarenka are the dominating favorites for the period just ahead.
 
Serena Williams (odds 7-1)
 
Serena won Garros in 2002 and reached the semis the next year, but she has never again passed the quarters. At age 30 and having been largely inactive for much of two years because of injury and illness, she seems unlikely to obtain a new Slam crown on the Garros clay, where the effects of her potent serve and strokes are diminished. She remains an intense competitor, however, who after extended absences can rebuild her strongest game as tournaments proceed. That seemed the case in her winning the clay event in Charleston earlier this year. Serena won her last two matches there, defeating Stosur and Safarova with loss of only a total of three games.
 
THE OTHERS
 
Petra Kvitova (odds 7-1)
 
Kvitova is probably the only current player able to contend with the relentless power of the aforementioned three, which she can preempt or answer with equal power of her own. Now 22 at height 6-0, Petra won Wimbledon last year behind potent left-handed serving and stroking. She is most effective indoors, where her sliced serves tail viciously leftward. During matches she sometimes has error-prone spells that come suddenly, often when she has seemingly established clear dominance in the play. At Stuttgart Petra lost both sets to Sharapova though her scores were better than Azarenka's when Vika played Maria in their next-day final.
 
Four Recent Garros Champions
 
The champions of the last four years at Garros were all surprise winners. Two of them -- Ana Ivanovic and Svetlana Kuznetsova, the winners in 2008 and 2009 -- are still fairly young. They played each other on indoor clay in April Fed Cup action, Kuznetsova winning closely. Both seem on recent upswings, but neither seems ready for consecutive wins against today's top ten. (Odds for each, 100-1 or longer.)
 
More plausible are the candidacies of the last two Garros champions. Francesca Schiavone, now age 31, and Li Na, now 30. Seeded only #17, Francesca won the 2010 crown behind a splendidly athletic and varied game not reliant on power. Last year she again reached the final but could not overcome the heavier and relentless shot-making of Li Na, now 30. The Chinese star had earlier scored straight-set wins over both Azarenka and Sharapova. Li has shown some good wins in 2012 to date, and a strong run by her at Garros this year can be expected. (Odds Schiavone 40-1, Li 20-1.)
 
Artists, Not Thunderers
 
--Agnieszka Radwanska (odds 20-1), now aged 23 at 5-8, has risen nicely in the rankings since about a year ago. Hers is a game of well-controlled firmness backed by excellent movement. She won the title at Dubai this year and won the Premier Mandatory tournament at Miami, defeating Sharapova in the final. Revealed in her loss to Azarenka at Stuttgart was her problem against a stronger and aggressive hitter who refuses to provide unforced errors.
 
--Caroline Wozniacki (odds 40-1). Now aged 21 at height 5-10, Caroline finished as the officially ranked world #1 in both 2010 and 2011, displaying a knack for error-free play as close matches approached decision. Her softish game has now been stepped up in power, both in serving and stroking, but she has slipped in the rankings in 2012, not yet comfortable in employing her heavier hitting against the top players. As the youngest member of the world's first twenty, her potential for again reaching #1 seems obvious. She lost in the second round at Stuttgart.
 
Also Dangerous
 
--Samantha Stosur (odds 20-1). Sam, 26, is the current U.S. Open champ. Hers is a firm, forceful brand of tennis, a style not especially favored on clay, though she reached the final at Roland Garros 2010 in a run that included wins over top-seeded Serena Williams, three-time Garros champion Justine Henin, and past world #1 Jankovic, In the final against Schiavone, however, she failed to summon her preceding high level of play. There have been only a few successes in 2012, but she pushed Sharapova to the limit in Maria's path to the crown at Stuttgart.
 
Not to be ignored are Marion Bartoli and Jelena Jankovic, both 27. Bartoli reached the semis at Garros last year -- her best-ever Slam finish -- following a strong run at the tune-up in Strasbourg. Coached by her father, who is a doctor, Marion is a determined competitor who ended Azarenka's 2012 streak. Jelena Jankovic finished as world #1 in 2008 but since then has drifted out of the first ten. In April, she scored two singles wins in Serbia's 3-2 Fed Cup victory on Moscow clay. (Odds Bartoli 40-1, Jankovic 100-1.)
 
Germany's Risers
 
Again sidelined is Andrea Petkovic, 24, who penetrated the world's first ten last year but severely injured an ankle during play in Stuttgart. But there is a host of other, young German risers threatening to move further upward. Angelique Kerber, age 24, Julia Georges, 23, and Sabine Lisicki, 22, are all inside the world's second ten. Then there is tall and powerful Mona Barthel, 21, who beat Ivanovic and Bartoli at Stuttgart before losing closely to Azarenka, thereby rising to rank #31. (Odds for each 100-1 or longer.)
 
Kiki Bertens
 
At age 19 and height 6-0, Netherlands player Kiki Bertens won the tournament in Fes, Morocco, last week. In winning all eight of her matches including three in the qualifying rounds, Kiki leaped into the world's first hundred. Her victims included three players in the top hundred along with two others currently appearing on our watch lists of risers.
 
Kiki's serve and backhand are capable of sudden strikes, but her greatest asset is her forehand, which flows with easy power from her strong physique. Her triumph at Fes should assure her entry at Garros if not at Madrid and Rome. Surely she has earned early admission to our next watch list. (Odds for the forthcoming events, astronomical.)
 
ARTISTS vs. THUNDERERS
 
Our four leading candidates among the women -- Azarenka, Sharapova, Williams, and Kvitova -- epitomize the thunderers in considering today's tennis on clay. At the next level, Li and Stosur too seem largely of that same population, while Radwanska, Wozniacki, and Schiavone seem of the artists. Most of the others are even more difficult to fit into our classification, though the German and Serbian women along with Bartoli seem in the direction of the thunderers.
 
A similar picture among the men, with Isner the arch-thunderer, likewise points toward a conclusion that we posed at the start -- that some ability in wielding power is essential for success at the top levels. The varied artistry welcomed by galleries has limited value if the serving and stroking are soft. The modern pro game has made superior thunder -- whether applied relentlessly in neutral rallies or in extreme degree when making the strike -- typically the most important decider in matches. The intelligent delivery of superior power without excessive errors has become a path to winning on clay as on faster surfaces.