The film is the tale of the underdog only in a way. Billy Beane (the Pitt character) is a general manager frustrated because, as a coach at a small-market (Oakland) team, his budget is a small fraction of the Yankee budget. His team makes the playoffs nonetheless, and his reward is for other, richer teams to seduce away his best players with lucrative offers. It's terrible that baseball success is that determined by team budget, the thought is.
So Billy—a real smart guy who turned down a full scholarship to Stanford to sign a baseball contract—counters money with science. He brings in Peter Brand (the Hill character)—a Yale economics grad with an obsession with baseball statistics—to choose bargain players neglected by other teams for reasons having nothing to do with the actual wining of games. He's going to take advantage of what Brand calls the "epidemic failure" to understand the real causes of victory and defeat in the game.
Now Brand doesn't invent the statistical model that drives the innovative player selection. That was done in a book by the hyper-nerd and horribly socially maladjusted Billy James. But no team had ever applied the method consistently, because they all were in the thrall of the apparently wrong romantic premise that you can't reduce the personal art of the sport to an impersonal science. It turns out that the scouts, with all their experience, have no idea what they're doing when it comes to selecting players.
The statistics that govern the rebuilding of the team are amazingly simple. Players are chosen pretty much for their knack for getting on base. Stuff like fielding turns out to make little difference. Counting the team's collective capacity to get on base turns out to be like counting cards in blackjack. It won't determine the outcome of a particular hand or game, but it's a method pretty much guaranteed to get results over a whole season (like over a whole night at the table).
This victory for the little guy is not a victory for players. They're treated like cards, traded or not according to the results of printouts. Even Brand complains that fans won't understand why an all-star is being traded in the middle of the season, but Bean doesn't care. His goal is winning, and it turns out that's all the fans end up caring about. It turns out that the scientifically detached general manager (who won't travel with the players for fear of getting attached to them) can gain rational control over the game. The owner of the Red Sox is impressed enough with the success of Beane's small-budget team that he offers him the largest contract ever for a general manager to come to Boston. He's worth it!
Beane doesn't come to Boston. But the Red Sox had already hired James anyway, and the statistical method governed the selection of the 2004 team that won the World Series—the one that broke the curse of the Bambino. Science defeated superstition!!
The film, thank God, is nowhere that simple. Baseball is saved from science, to some extent. Beane is quite superstitious; he doesn't watch Oakland games for fear of jinxing the team. The team wins 20 games in a row, but the truth is no science would have predicted that! That streak has the mark of irreducible randomness about it. Beane decides to go ahead and watch part of the 20th game in that streak when he finds out the As are up 11-0. Incredibly improbably, the other team actually catches up and the score is 11-11. There's something to the superstition!? Well, no. A miraculous or at least somewhat improbable homer wins the game for the As 12-11, and that victory is just as good as one won 11-0.
In any case, Beane recognizes, baseball isn't about the regular season. People don't really remember a team unless it wins its final game (in the World Series). And there just aren't enough playoff games for the science to work. The outcome of the key part of the season is pretty random. The scientifically constructed As are taken out by the Twins in the first round of the playoffs.
We also learn from Beane that he is quite ambivalent about being romantic about baseball. His own life story has filled him with "issues." He turned down the Stanford scholarship because scouts told him that he had all the skills required to be a baseball star. But—due it seems to some deficiency in character more than talent—he never made it as a player. The romantic dream of becoming a legend—a role model of personal excellence—didn't become real for him.
Scouts, in turns out, don't KNOW how the career of any of their recruits will play out, and Beane blames them for not being scientific enough to KNOW. But even the statistical science of basebell can't predict with any great degree of reliability the fate of any particular career. The science depends on aggregate results. Beane seeks rational control out of resentment, and even out of envy for those with both the character and talent to be stars.
Billy's shy, emo daughter, at his urging, sings a moving version of the song "The Show." It's an emo tune that was featured prominently in the emo classic Juno. It came out in 2008, and so the key role it plays in the film is strikingly anachronistic. Billy, the dad, seems unduly moved by it. Listening to it, apparently, kept him from taking the Rad Sox's incredible offer--just so he could continue to play a big role in his daughter's life. He chose to be a dad, a man. He chose, not exactly romantically, for real life.
Baseball is a child's game, we learn, that some men get to play until they're 40 and a few can stay involved in longer as managers, general managers, and so forth.
"The Show," of course, is the name all professional baseball players give to the majors.
Billy's daughter changes the concluding words of the song to "You're a loser dad. Just enjoy the show." (Approximate quote.) Only a loser would try to gain rational control over a child's game.