Yep, it is all about head placement when you go in to tackle - if you are coming in from the side, your head goes behind the waist, ar$e or thigh. If you are tackling front on, you make sure your head is to the side of the hips, waist - I learnt this stuff as a 6 year old.
I destroyed both my shoulders from tackling (was a hooker for most of my time playing, when hookers actually 'hooked' ;)) but I never got a concussion from tackling...plenty from stiff arms and the old second rower upper cut in the scrum
, but never from a tackle.
And DeBelin is a text book exponent of it - the shot he put on Sione was a perfect example that would have knocked the ball loose on anybody...of all the dropped balls last week, I didn't find much fault with Sione for that one - just bloody good defence.