A boxing referee turned into a human punching bag on Tuesday ... getting hit in the face multiple times as he tried to break up the action -- but surprisingly, he took it all like a champ!!
It happened at the RIZIN 49: Decade event in Saitama, Japan ... where Rukiya Anpo -- who was originally scheduled to fight Ryan Garcia -- took on K-1 champ Sina Karimian in the bout.
The sixth and final round of the exhibition got intense when Karimian landed an illegal spinning back fist on Anpo .