Discussing The Blind Side: Evolution of a Game by Michael Lewis, Jason Kottke suggests a fascinating idea:
Many of the left tackles that Lewis talks about in the book can run faster than most quarterbacks, they can throw the ball just as far or farther (as a high school sophomore, Michael Oher could stand at the fifty-yard line and toss footballs through the goalposts), possess great athletic touch and finesse, have the intellect to run an offense, move better than most QBs, know the offense and defense as well as the QB, are taller than the average QB (and therefore has better field vision over the line), and presumably, at 320-360 pounds, are harder to tackle and intimidate than a normal QB. Sounds like a good idea to me.