Mersey Radio

Regarding a School Rugby Match with teenagers I heard a player deliberately kicked the head of a player in the opposition team when tackled to the ground by several players. The victim had concussion and was eventually taken to hospital, the brutal (in my opinion) player was given a yellow card. Is this action acceptable or should the player be banned for 2 seasons or even entirely from the sport. If this happened in the street a prison sentence would be the course of action.