I watched all 3 times (including this video) where he suffered a concussion and each time he lands on the back of his head. The second time against the Bengals seemed unavoidable because the defender threw him down with force. I just wonder if he is someone who doesn't know how to brace himself properly when getting taken to the ground. I'm not trying to be insensitive. We've seen NFL QB's before who genuinely didn't know how to slide properly when running with the ball. There is a technique to everything. That's just my observation, however.