Add to this that the OL is allowed to push you in the back as soon as you get by them.
It's one of the more hypocritical rules in the league: in a move to protect QBs, defensive players have to hit to a strike zone, and really control their momentum. At the same time, OLmen are allowed to push DLmen in the back, many times propelling them towards the QB out of control, and out of any semblance of control they would have had.
I can't tell you how many times I've seen DL pushed to the ground from behind once they get by the OT. I also can't recall how many times a guy has been pushed into a QB, then flagged for it (and recently, fined for it), but it's a LOT.