This video demonstrates why many of the skills developed by traditional martial arts sparring do not transfer to self-defense. The victim, showed good offensive and defensive aggression, when sparring in a controlled setting, against an opponent he was mentally prepared to "fight".
But when he is assaulted by a "surprise" attacker in a manner similar to a street attack, he is defenseless. After receiving the initial strike, he falls to the ground, and does nothing to defend himself against the attacker's followup kicks.
The referee attacker, despite years of traditional karate, finishes his victim with a soccer kick to the face, and a stomp to head in true "street fighter" fashion.