What pops into my mind is how many times he just got drilled his first year with Dallas. He took shot after shot and continued to line up and play.
For being a QB, he was one tough cookie.
I remember when Wilbur Marshall, then with the Skins, came up well after he had thrown the ball, kind of squatted down and just exploded upwards, drilling the crown of his helment into the chin of Troy. Gave him a concussion (maybe his first in the NFL) and split his chin so bad that he forever wore the cushioned chinstrap from that day forward.