Jumping bean

"He's a flying jumping bean, a bundle of hyperkinetic energy, with the tour's quickest hands. Still, he's never learned to hit a tennis ball. He hits off-speed, hacks, chips, lobs -- he's the X of Y. Then, behind all his junk, he flies to the net and covers so well that it all seems to work. After an hour you feel as if he hasn't hit one ball cleanly -- and yet he's beating you soundly."

Questions: Who wrote this? About whom?

No Google/Wiki/Bing/whatever. As they apparently say in quizzing circles, this is "workoutable". Eminently.

Extra credit: What is X, what is Y?