Weird, I heard that he was really smart and only played football because in nebraska you are a nobody unless you play football. He was actually going to quit earlier but his wanted to make his dad proud and his GF really wanted him to keep playing, plus he really liked his fellow team members.
Once it came out that he was possibly going to be second string he got worried about having to be "The Big Man On Campus" and fending off women left and right while focusing on his studies.
Deep down he is a coward and knew he wouldnt have the balls to stand up to Snyder shooting Huberts knee's up with dope after CK got hurt so he just said F this noise, I'm going home.