Cowart plays bigger than his size, he could be the backup-ish NT. He didn't inspire much confidence with his preseason play the last week or two, but OTOH I kinda suspect that Belichick might not be looking for a straight apples-to-apples NT backup since it's already a two down role anyway. If he was, we could've just kept Pennel. Belichick may find more value in having the backup be more of a tweener- a guy who can step in for Shelton a bit if he gets banged up, but also has a little more versatility to contribute without Shelton needing to get hurt.