When guys are hurt or just coming off of injury - they just don't play like they do when they're healthy, particularly when they're young. When a player doesn't "feel like themselves" ... then they likely won't play like it either. I imagine that many of us remember Jermelle Lewis and how impressive he was capable of playing. What he did against Michigan in 2002 will forever be seared in my memory.
However, if you observe his play in either of the subsequent seasons ... when he was coming off injuries ... his play in either '03 or '04 was a shadow of what it was back in '02. Admittedly, he wasn't running behind the same quality lines the latter two years ... but he simply didn't have the same explosiveness or "slashing" ability that he had in '02.