It's clearly possible to jump over a pile of players who are set up to defend a plunge into the line; that's why backs like Turner use the leap as a change of pace. The question is whether a high jumper could get up far enough that a defender who knew what was coming couldn't stop him. It seems plausible. NFL defensive linemen top out in the six-and-a-half foot range and need to crouch slightly to stand their ground against blockers. The crowns of their helmets are likely no more than six feet off the ground. World-class high jumpers regularly clear seven-and-a-half foot bars; the record is a little over eight feet.