What if he had pulled the weapon before he was touched, then fired a warning shot into the ground? If illegal, why? His shot scattered the threat.
Department policy varies slightly in areas of California, but generally a police officer may unholster a lethal weapon when he perceives a possibly quickly executed threat to human life or great bodily injury, and he may point the weapon when he perceives that threat from a particular individual or location.
To deliberately discharge a lethal weapon the officer must perceive a movement or situation that indicates execution of threat. Unfortunately these rules and policy proscribe "warning shots" or deliberate shots to disarm, as the officer must fire to ELIMINATE the threat to human life.
By training and policy that is shooting to center of mass/chest in a pre determined pattern, if possible.