It has to have something to do with the physical nature of the game. The getting off blocks to make a tackle. The constant chasing of a wr around then having to make a play on the ball or receiver. Play after play. I kinda equate it to driving nail....Hammering a few things won't really be a problem for most, framing an entire room...or doing it all day...man your hand gets tired. And you don't really know that until you try it. Sure after a while, you have a grip of steel, but what if you never had to push yourself? 93 plays...I've seen games where most defenders play 40 plays. 60 plays is rough. And again, the offensive line is used to never leaving the field. The only player on our defense to play every snap was Alex Ogletree. Isn't that strange? I think the list of the guys that did this had 10 players....4 or 5 were QB's.