He's a great player and did sacrifice for his team but the timing of his decision warrants some boo's. On top of that, I'm sure for many fans it seems as though he's quitting on them.
The culture of football is that you play until you can't. When it seems like you're still young enough and capable of playing but you choose to quit? That isn't going to set well with many.
In this particular case, I'm sure it is mostly the timing and shock of the situation. To go from an all-pro year and playoff victory last year to just up and quitting is a pretty tough pill to swallow.
