The QB made the decision to slide TOO LATE.
Don't watch it in slow motion, watch it full speed, and watch GJ.
It was 3rd and 9, the QB takes off full speed running strait up, doesn't "give himself up" until
42:58 play starts
43:03 players are 7 yards away, QB is running full speed and GJ has started to break down so he doesn't get juked
43:04 Players are two yards away, QB begins to slide, at this point GJ has already pushed his momentum forward to go for the tackle at the waist. Right here, if he goes "high" that is a penalty for going helmet to helmet, so he goes low.
still on 43:04 all this happened within 1 sec, he broke down, went for the tackle as the qb was sliding and made the contact helmet to helmet
If the QB is allowed to give himself up, he should do it before the defenders are two yards away. If the QB is protected from getting hit, he scrambles and becomes a ball runner without the ability to hit him as you tackle him, they should just call him down as soon as he's touched. Put a different color jersey on the QB and protect him from getting tackled in the open field. Because that is all GJ was trying to do, is not get beat in the open field, so he broke down and went low. The QB drops at literally the last second, when GJ is two yards away, and this is what brought his helmet down to the level where GJ is going to hit him.
It's tough to impossible being a defender against a running QB, if you are going to get thrown out of the game for trying to tackle the guy, because he can "give himself up" at the last possible second. It's a bad rule, if the QB doesn't give himself up with defenders 4 or 5 yards away, they are already going to be initiating the tackle, so that extra yard he's trying to pick up for the first down isn't compatible with "give yourself up". Can't have it both ways.