That's really dumb. Making contact with the head, hello concussion and more head injuries. Also, allowing a OL to get into your body makes it easier for them to hold you and get away with it. Our DL should be firing off the ball and using their hands to keep blockers off of them. It's no wonder our DL essentially sucked last season.
Unless you get hit under the chin or speared in the side of the helmet
you're probably not going to get a concussion form hitting heads on the line.You really dated yourself with the head slap comment, that's been outlawed for a long time. It's probably a better way for someone to get a concussion than "head butting", which is probably a poor choice of words by Cam. I think they are probably being taught to make first contact with the helmet more so than head butt the guy.
If you look at any outstanding middle linebacker or D lineman you'll notice that there helmet is scarred up pretty good and it's always from making contact with the other guys helmet. We were always taught that when shading a man to attack the offensive lineman in the V of the neck in the direction we wanted to control. Essentially attack leading with the head up into the armpit just under the chin and your hands on his breast plate inside and outside, once you make contact you basically bench press them to get separation and control, and shuck him when you know where you need to go. The point of leading with the head is to gain more leverage. If you come in lower than your man with your head up you have all your momentum concentrated in that small area and it's much easier to drive up and through him and hopefully knock him off balance so you can have your way with him.
So jsneb83 is right it helps to create separation and reestablish the LOS, but I would argue *WARNING SCIENCE AHEAD* that you generate more Power (Power = Work/Time) by engaging with your head and then pressing the defender away because you have increased the amount of Work (Work = Force x Distance) done by increasing the distance over which the Force was applied (Force = Mass x Acceleration). Nerdy I know, but football is all about physics.