The NFL is a tough business.
You get hit or you hit until you are concussed. You break bones and are expected back as soon as they heal, and your contract isn't worth the paper it's printed on.
And to top it off, being named the starter doesn't mean anything past the week you just played.
Brandon Jacobs thought his spot was solid as the New York Giants starting running back. But that doesn't seem to be the case anymore.
Here's a list of other players whose starting days might be numbered.