15. Mark Sanchez
The New York Jets thought that they had themselves a future legend in the mold of Joe Namath. But that turned out not to be the case, as Sanchez started well but went into severe decline. He had three decent seasons at the top before the doubters made their voices heard and his career went into a downward spiral.
Sanchez did make an impact on the Eagles after Nick Foles suffered a serious injury. But from then on, teams consigned him to life as a back-up. Finally, he started just three games in his last three seasons as a professional. It was quite the fall from grace.