Clay is great at everything except run defense. Great pass rusher, hugely underrated in coverage, great in pursuit from behind, but on runs made right at him he is a little cavalier in reponsibility holding the edge, and even when he does, too often, he gets handled by tight ends.
That was one of the reasons behind drafting Perry - he's stout enough to set the edge in the run game
Funny enough, that is the only thing Perry for well.