It's a characteristic that, if found in the wild, would assure the extinction of whatever species possessed it. It's an unwillingness to release a grip once acquired (except to secure a superior grip), regardless of the degree of bodily damage taken in battle. Naive people mistake the observation of gameness in practice with "locking jaws." The jaws don't lock. The Pitbull merely refuses to let go. Now, a Pitbull trained to a release command will release on command, but that's not a statement about its gameness. Gameness is the refusal to let go due to damage, not the refusal to let go in response to a command, assuming the dog is trained to such.
Pit fighting professionals never train their dogs to let go on command, since this training operates counter to their purposes, and opt for breaking sticks instead, which are wedged between the upper and lower teeth and worked back towards the molars till the grip is released and the dogs are separated.
