Superhuman? Right hand punches left hand, probably something iconic that happens on a regular basis. This time, it goes wrong. 
Right hand punches left hand.
Too much force.
Left hand snaps back, breaking wrist and fracturing some knuckles in right hand.
Veins in left wrist burst violently.
There's blood. A lot of blood.
Initial impact also caused tremours along the arm, dislocating both at the elbow and the shoulder.
Excessive blood loss causes weakness, difficulty thinking and seeing.
This eventually leads to unconsciousness, followed shortly by death.