Originally Posted by Johnny Footstool
He walked away from a good portion of that money.
He got fed up with Mike Brown, and he asked to be traded. Brown refused, so rather than take the money and go through the motions, he quit.
Actually, he already got a lot of his money before he played a down. Signing bonuses are the best kind of guarantee because its money in hand before you've been asked to perform. In contract law, that's called consideration, which means once you take that money, you have a duty to perform the contract. The way NFL contracts are actually constructed, the signing bonus should be considered the real compensation and the so-called "salary" is really a performance bonus.
In the real world, if anyone of us signed a contract paying us up front and refused to perform, we would be sued civilly for breach of contract and could also be charged with theft. On top of that, our employer could even prevent us from working for competitors for the length of the contract.
If NFL players wanted more flexibility in deciding when they can leave a team, they could alway just sign one year contracts and renegotiate every year.