Here's a wonderful video essay written by Dipnot.tv film critic, Far-Flung Correspondent, House Next Door contributor, longtime Scanners commenter and International Man of Mystery Ali Arikan, and edited by writer/photographer and Press Play producer Ken Cancelosi. As far as I'm concerned, it makes the case -- and does so even without including my personal favorite scene from "Moneyball"! (I think he should have been nominated for supporting actor in "The Tree of Life," too.)
There is real mystery to Pitt's take on Billy Beane. He loves the game, but knows the game is changing. He knows he has to get wins in order to keep his job, and is more than willing to modernize for that reason. But he also knows there is something you can't calculate about the game of baseball. The scenes of Pitt driving to work or sitting in the locker room show a man who is constantly trying to figure out the odds and knowing deep down that there are some things you can't figure out.
... He brings to the role an assured quality on overzealous, yet understated, lust for ultimate success that was forged in the fires of years and years of failure. He's charming and cheeky and funny, and very good looking (despite the hideous early naughties' haircut and lumbering fashion sense). Pitt brings a subtle comedic take to what could have been a rather boring central role; his various dealings with other managers, his scouts and players, betray genius-level timing and mimicry.