Just a correction. The fat guy wasn't from his team, he was from some other team. And he didn't fall, he jumped down onto the first base because that's what he was only barely able to do, he knew that in the best case scenario he only have like 50% chance for the first base because he run so slow.

So basically his tactic was: if I run as fast as I can I have 40% to reach first base. If I run as fast as I can and jump I have 50% to reach first base. He didn't even consider going to second base, ever.

Moneyball is great movie, go watch it.