In MMA -
This is a demonstration of respect
That probably clears things up for you. :0008
Antonio Inoki..
from Wiki:
"During one visit to a school in the 80's, Inoki was punched twice by a student. Inoki slapped the student across the face, knocking him down. The student, who later turned out to be an Inoki fan, then rose, bowed deeply, and thanked Inoki for the slap. The incident became very famous as the then live clip of the binta (slap in the face) was shown many times on Japanese television. Now various celebrities and even common people in Japan ask Inoki to slap them to install courage or even as some sort of strange blessing. The slap's name is the "Fighting Spirit (or Toukon) Slap."

