A plainclothes UCF officer was killed in Orlando, in somewhat similar circumstances, a couple years ago. Drew a handgun when several drunk students resisted arrest, after one or more physically assaulted him.
A county deputy saw the brawl and approached. The UCF officer either didn't hear or failed to respond to the deputy's commands to drop his weapon. The deputy fired...
This sort of thing is tragic, but understandable. It reinforces the need to have a plan as to how to react when LEOs arrive, and for CCW types to be absolutely certain they know the situation prior to involving themselves and a weapon.