Ask HN: Any good open source sports games?

Despite the fact that most devs at one point or another have wanted to do a game -- and sports games are among the best selling -- why are there no open source sports games?

I was looking at the trailer for NBA 2K12 and just awestruck by how nice it looked. I thought for a second, maybe I could spend some time and contribute to an open source version. Alas, there's really nothing.

Does anyone know of a good baseball, basketball, football, soccer, hockey open source games?