A scholarship is a contract. Iowa State offered him a year of school for his services to the football program. The reason players get away with it is because it would be PR suicide to revoke the scholarship.I am going to throw out a crazy thought. He is a human being. He didn't know 100% what he wanted at the beginning of the season. He was already on the fence, things weren't going well, he picked a different path.
In terms of him "signing a contract," he clearly didn't, otherwise there would be lawsuits every time a player left the team for breach of contract.
You signed the scholarship. You hold up your end of the bargain. End of story.