Wrestling and boxing

From: Greece
Date: about 500-475 BC

The ancient Greeks encouraged young men to be fit and take part in sporting competitions. The two naked fighters shown on this cup are in the middle of a pankration, a sort of wrestling match in which nearly anything was allowed, including kicking and strangling. The only fouls were biting and trying to gouge out someone's eyes.

The referee is about to hit one of the fighters for cheating. Which rules do you think he is breaking?

There is also a pair of boxers next to the pankratiasts. You can see cuts on the face of the right-hand one.