Let's just say for the sake of my writing that the subject complies. Do you then run up, dive on like the typical dog pile, and engage in a wrestling match to try to restrain the subject by yourself? No, you do not. You take up a position of advantage (that means where he can't see you and you can see him) and keep him covered to await your on-rushing back up officers.
You did call for them on your radio, right? Ok, so you have Billy Bad Boy on the ground, you have a tactical advantage and he is submitting to the surrender ritual by remaining there as you cover him with your firearm. You do not know if he has more weapons or if he intends to fight further. If your back up is on the way, why chance it?
Off duty, you are in somewhat of the same boat but at a severe disadvantage. Remember, you are still not wearing your vest or uniform. You have intervened and, again for the sake of the argument, let's say Billy complied. You do as you are trained by taking cover, and keeping Billy at a disadvantage.
What now since you do not have a radio? How about that new invention called the cell phone? Call your local 911 operator and tell them what you have going. Be sure to tell them that you are off duty and what you are wearing so your on-duty brothers don't shoot you when they arrive. Now just wait for the cavalry.
Remember, in situations that may involve such force, others are also going to be calling the police as well as filming you with their digital cameras on their cell phones so be prepared to accept that the police are being told, There is a guy with a gun and he is threatening to shoot some guy on the ground by the other people calling. After that, expect to see yourself on You-Tube or some other such site.
So, why exactly do I need to carry all kinds of police equipment off duty? It sure isn't to restrain the subject; that is what on-duty officers are for. It would be nice to have the stuff, but my wife, and I would venture to say, most wives would cease to go anywhere with a husband/officer who looks like he is ready for tactical assault. Further, there is no law that says that any citizen who chooses to become involved in such a situation has to take the next step and restrain the bad guy if said bad guy chooses to comply. There! The attorney's argument is null and void.
If we try to act like John Wayne (sorry Duke) when off-duty we are going to get hurt. Are you going to get duty disability when you intervene in something off duty that leaves you injured to the point of not being able to work? I doubt it very much.
My friend told me of another story that he had read about where an officer was driving and just ahead of him, he observed a carjacking in progress. The offender had a handgun pointed at the driver of an SUV and was screaming for him to get out of his car.
Due to the severity of the situation, the off-duty officer, a few cars back, exited his vehicle, took a position of cover, drew his weapon, and yelled the standard, "STOP! POLICE!" at which point the offender began to turn his weapon to the officer. Bad move for him as the officer had the guy already sighted up and dropped him without any further damage.
Was he supposed to restrain this guy? The offender's actions precluded any chance of that. Were the officer's actions offensive or defensive? I would argue defensive as our actions most of the time are. We have to react to the actions of the offender before we can take the actions that ultimately stop the situation. The officer acted as any citizen should have that is licensed to carry a firearm. He acted in defense of another's life and ended the situation with only one person getting hurt, the person who started the whole confrontation. Let's keep the blame where it is supposed to be, on the offender.
Carry what you feel comfortable carrying when off duty but by all means, use your head if you are faced with a situation that might call for the police. If it is of a nature that does not require immediate use of a serious amount of force, make the call and be that good witness. If it is a situation like our two cases noted above and you have to be involved, do so with the clear headedness to defend yourself when the street battle is over and the court battle begins.