Quarterbacks are generally considered fragile and prone to injury.
Of course some of this is related to the vulnerability related to getting blindsided while they are throwing the ball. However, this injury concern extends to when they are expecting the hit or running with the ball - to the point that we expect the QB to slide in open field. During training camp they wear a special jersey to indicate "don't hit me!".
I used to think this was because QB's were smaller, but not so sure. They are not as built like a linebacker, but they are often bigger the a WR.
So why is it that QB's are more prone to injury and carry the stigma of being fragile?