Boxing

In general, boxers are prohibited from hitting below the belt, holding, tripping, pushing, biting, or spitting. The boxer's shorts are raised so the opponent is not allowed to hit to the groin area with intent to cause pain or injury. Failure to abide by the former may result in a foul. They also are prohibited from kicking, head-butting, or hitting with any part of the arm other than the knuckles of a closed fist (including hitting with the elbow, shoulder or forearm, as well as with open gloves, the wrist, the inside, back or side of the hand). They are prohibited as well from hitting the back, back of the head or neck (called a ``rabbit-punch'') or the kidneys. They are prohibited from holding the ropes for support when punching, holding an opponent while punching, or ducking below the belt of their opponent (dropping below the waist of your opponent, no matter the distance between).

Question: is it legal to punch the back of the head in boxing
Answer: no