Just a penalty?

South Africa run with the ball and fullback Zane Kirchner comes into the line. Conrad Smith tackles Kirchner from behind and as he does so Rene Ranger (11) of New Zealand crashes shoulder first into Kirchner.

The assistant referee puts out his flag and tells the referee that the tackle should be lower and that arms should be used. Ranger is penalised and told to use his arms.

Law 10.4 (g) Dangerous charging. A player must not charge or knock down an opponent carrying the ball without trying to grasp that player.
Sanction: Penalty Kick

There is the difficulty that referees and assistants referees have of needing to make an instant decision but high and armless is pretty damning.

Certainly it was a more violent and dangerous act than that for which Danie Rossouw was sent to the sin bin.