[self_assembly]

By not continuing to pummel him when he is on the ground. I don't know what could compel someone to continue hitting a person's head as he lays helpless on the ground (the opponent was basically curled up in the fetal position). At that point it just seems like the fighter gets some sort of sick enjoyment from hurting the other person.

[echlebek]

The referee is supposed to stop the fight when one of the fighters becomes unable to defend himself.

[self_assembly]

Sure I get that. But how far do you take that justification? Would you be willing to kill someone who is laying on the ground defenseless because the referee is inept. Fighters need to have some self control. And it in this specific situation it seemed pretty cut and dry that the Tai Chi master was not able to fight back.