[LaFlamaBlanca]

First of all, I think the obvious reason is safety, and more specifically, for the safety of the kids on defense. Secondly, lets not overplay the issue of a kid being over the weight limit and "stuck on the o-line." I find it hard to believe that a freshmen football coach is going to look at a player and say, "well he was a linemen in the little league, so he was to be one on the freshman team." On my freshman team, alone, there were two RB's, who were RB's from 3rd grade through 8th grade, only to be put on the d-line freshmen year. Conversely, there was at least one, maybe two, offensive linemen/ "blocking tight-ends" in little league but were freak athletes and converted into a QB and RB. So, lets not act like weight limits force kids to be stuck in positions throughout their high school careers.