A kidney punch is a punch targeted directly at a person's kidney. Because of the potential for serious injury, kidney punches are not allowed in the sport of boxing, according to BoxRec.
A punch to a kidney can severely bruise and cut the kidney. An especially strong kidney punch can cause a kidney to tear loose from blood vessels. Damage from a kidney punch ranges in severity from very mild pain to bloody urine, anemia, shock, kidney failure and, in the worst cases, death. A person punched in the kidney who experiences lasting pain or bloody urine should seek immediate medical attention.