Have you ever been attacked by a Pit Bull or seen the results of an attack by  a Pit Bull??  They don't bite & run they bite and hold while shaking so even more damage is done. many times the animal may be really calm & nice with Friends or family and show major aggression to anybody else. Its a fear syndrome & instinct kicks in and that's why the animal broke its chain.  Anybody who travels with dogs should know the rules about allowing the animals into certain areas while keeping it under control. Many insurance companies are now "not" insuring homes with Pit Bulls,  I wonder why that is. Hmmmmmmm   What if he had gotten loose and went after your 4 year old daughter???? would you have shot if you had a weapon??? or would you have wanted the security guard to stop it before damage was done.  We all love animals but its the owners responsibility to use common sense
and control the actions by restraint if needed.