Being a reserve S.O. Deputy, I would take cover and engage the BGs with my handgun, on or off duty.
If I wasn't a LEO and had a firearm with me, I would do the same. I will not stand around and watch a Officer get gunned down. Unless he is Jason Bourne, he will have problems with 4 bad guys shooting at him.
Training scenario? not likely, there would be police barricades and yellow police tape around the perimeter, or something would be there to alert people to the training.
The Post, Houston, TX
In the finest tradition of armed citizens who take on crime in their communities, Texan Travis Neel helped save a wounded Harris County deputy sheriff's life. Witnessing the shooting by one of a trio of Houston gang members after a traffic stop just west of Houston, Neel--who was on his way to his pistol range--pulled his gun and fired, driving the officer's assailants away. An off-duty sheriff's deputy also came on the scene and joined Neel in covering the deputy, whose life was saved by his body armor. The trio was captured after a manhunt.
I work at the same Dept. I was in Communications, but I was off that day. One of the gang members hid in the back seat area of the SUV and later jumped out and started shooting at the Deputy. He pulled his gun and returned fire and his Glock jammed on him. He crawled under his police car to try and avoid the rounds. He was hit a couple of times. The citizen pulls up and steps out with, i believe, a CZ 75 9mm and shoots at the gang. They take off running into the neighborhood. an off duty deputy comes running up to aid the wounded deputy. a Massive manhunt ensued and they found the bad guys.
The Citizen got an award for saving the Deputy and I believe a Winchester Rep. presented him with a case of 9mm cartridges so he can practice his markmenship. He did scare off the attackers, but he didn't hit a single one of them.