At last year's World Rugby Sevens we saw several examples of where players were high tackled and/or having their heads twisted and then being bought to ground. Several players have been injured.
The tacklig above the shoulder line and twisting at all levels of the game is Dangerous Play and should be dealt with severely by referees.
The video clips shows 2 examples from the Womens Game. Players are correctly penalized and the video clips have the following law reference:
Law 10.4 (e) Dangerous tackling. A player must not tackle an opponent early, late or dangerously. Sanction: Penalty kick
A player must not tackle (or try to tackle) an opponent above the line of the shoulders even if the tackle starts below the line of the shoulders. A tackle around the opponent’s neck or head is dangerous play.
Sanction: Penalty kick
You will find more video clip examples at the Laws of the Game website.