Roger's Record
Federer has already won 10 majors: four at Wimbledon, three at the US Open, and three at the Australian Open. In 2004 and 2006, he needed only the French Open to complete The Grand Slam. If Roger can win Roland Garros this year, he stands an excellent chance of going ahead to win the remaining two, so the tennis world is unusually excited to see whether he can do it. Roger has improved his clay-court skills considerably since 2004, when he lost in the French Open's third round. Last year, he made it to the final, where he faced probably the only player who could have beaten him at that point, Rafael Nadal.
Nadal on Clay
Rafael Nadal has tremendous talent for playing on any type of tennis court, but his skills are most perfectly suited to clay. When a tennis ball strikes a clay court, it plows into the loose surface just a bit, forming a little ridge of clay in front of itself that both slows it down and makes it bounce higher. For Nadal, who can run down any ball, given half a chance, and who loves to hit heavy topspin, nothing could be better.
Federer hits relatively low, fast groundstrokes so well placed toward the sidelines that, on a faster surface, very few opponents can reach enough of them to keep up. Through the course of the 2006 Roland Garros, though, Nadal showed defensive capabilities almost beyond belief. Federer was far from brilliant that day, but even when he would make Nadal run the full 36-foot width of the singles court and then another 10 feet due to the shot's angle, Rafa would often not just send the send the ball back, but give it a severe angle and heavy topspin to boot.
Roger is incredibly quick, but not quite as quick as Rafa, and he has two other disadvantages on the clay: a one-handed backhand and less topspin.
Trouble with High Backhands
A one-handed backhand performs much better than a two-hander on low balls, but the maximum height at which most players can meet the ball to hit an aggressive topspin with one hand is significantly lower than that for a two-hander. On clay, where topspin shots bounce fairly high, that lower maximum height makes a difference quite frequently. Neither type of backhand can do much with the ball once it's above shoulder height, so one of the battles that often takes place within clay-court points is a contest to see who can make the ball bounce higher on the opponent's backhand side. If you can make your opponent hit a high backhand, he'll often send you a weak shot that you can put away easily. A two-hander has more chances to hit that kind of aggressively high-bouncing topspin shot from his backhand side.

