Interesting. I read an Ask Vic segment and he mentioned how the pro game changed , at one time, to favor the passing game as far as the offensive line was concerned. Faster, speedier lineman who could be effective in the pulling run game, because they weren't allowed to grab a defensive player, were built at a lighter weight. Then the rule changed and emphasis was on passing game where O lineman could get their hands on defensive lineman so the lineman of choice were big and tall. The players in those days, had to adapt as well. Trickle down had to occur then too, right? Those suited for line play, earlier, were no longer suited for it so they had to assume different positions. It's the evolution of the game.
