In a way, it more about what you DON'T need to a good hard court player.
You DON'T need the endurance to play the endless points clay can produce.
You DON'T need to be able to handle the ultra low bounces you can get on grass.
You DON'T need to be able the bad bounces you can get on clay or grass.
So a player with power, and some endurance, but who's NOT good at making last second adjustments, can be successful on hardcourts, even they aren't on clay or grass.
A spinning balls 'bites' into clay more. So players like Martinez, Henin-Hardenne and Schnyder get a payoff for their ability to use these shots on clay. The effect of the spin is magnified. Players who can't handle that, but who are otherwise good, do a lot better on hardcourts.
A ball simply hit with massive pace can skid on grass, barely rising after it bounces. So players like Sharapova and Davenport, who hit with big pace, and hit close to the lines, gain a big advantage on grass. The rest of the tour is killing themselves just to reach the ball. But on hardcourts, the ball doesn't slide through the court so much, and players who are a half-step slower can reach the ball.
It really comes down to fewer, and less variables for the players.
Why are some players at their best indoors? Fewer and less extreme variables. No sun in your eyes, no wind, consistent lighting, (usually) no insects, no airplane or traffic noise, the surface isn't ultra slow or ultra fast. Some players handle these variables well, some are affected by them.
A player who excels on hard courts, but NOT on clay or grass is, to an extent, defined by their deficiencies, not their assets. They may lack the endurance and consistency to excel onclay, or the footspeed and pace to excel on grass.
Grass maximizes Lindsay Davenport biggest assets, the pace and accuracy of her striking. It also exposes her lack of footspeed, but since she's usually in control of the point, that's not often a problem.
Clay maximizes Justine Henin-Hardenne's ability to slice and spin. Her opponents are dealing with the ball doing things they just aren't used to seeing. And since the ball coming off the surface slower, it allows Henin-Hardenne to compensate for her lack of height with footspeed.
There aren't many player in the top twenty who are only good on hardcourts. If you look at their records, you generally find they also go deep into tournaments on grass or clay.
Originally Posted by alfajeffster
Glucosamine Condroitin, a briefcase full of 800m Ibuprofen, and it helps if you feel the need to destroy your body. This tennis has in common with pro football.
This is also correct.