I was knocked out for a few seconds playing for Drunken Wasps at Fat Blokes 7s after being tackled in the air. Also landed on head and shoulder, after a deliberate foul tackle as I chased my kick ahead, where all 3 ACL ligaments ruptured and I next remember being asked if I was OK on the touchline some 20m away.
That was over 15 years ago and in both cases I can clearly remember before and after. I've had a few minor head knocks since then but nearly all have been at rucks. Just last season I got one jackling the ball.
To my mind, the law interpretation regarding tackling and foul play has been relatively successful but needs to be applied rigorously and consistently. Players and coaches will comply if red cards are issued frequently. Forget killing the game as a spectacle, to avoid that keep tackling low.
However, my point is that breakdown safety is virtually non-existent and that is where repeated traumas will occur. Flying off feet is insane. Should be a red card every time but is becoming a bit more prevalent again.
The problem is that ruck law changed and has made them static. Formerly a tackled player had to release the ball immediately and handling it was illegal so it was played back with the feet. The most effective way of rucking was to drive over the ball, putting the opposition literally in the back foot and creating fast dynamic ball. NZ and Scotland in the 80s were very accomplished at it.
Law 15.3 still says 'Players involved in all stages of the ruck must have their heads and shoulders no lower than their hips. Sanction: Free-kick.'
That means jackling is actually illegal.
Old fashioned rucking was abolished because players lying all over the ball preventing quick release got trampled on. It would be easy enough to yellow card them and reduce the prevalence and create more dynamic ball and enforce the current law. Head above hip ensures you see what's coming at you and keeps heads out if the way of the ball.