I suspect most of the time you can eliminate 300 of those 400 right away - they obviously are either too early or too late to capture the moment. On the remaining 100 you can choose any one (or more likely 5 as there are likely several moments - the moment the catch is made and the moment the athlete smiles as he realizes he made that catch).

The reason to take all 400 though as every once in a while one photo is obviously better than another for some reason. You also want several angles because sometimes the light will be wrong at the moment, or someone will happen to be in the way of your shot...