Didn't want to horn in on Tom Givens' 'Reminder' thread but I read something that warranted mentioning as a refresher.
This officer was killed during an off-duty intervention: https://www.odmp.org/officer/26107-d...ren-almendarez
It's difficult to discuss the issues surrounding any such encounter, without appearing critical or Monday-Morning Quarterbacking. I mourn Deputy Almendarez, we are diminished each time any person offers up their life in the service of the greater good, whether they be an officer, a service member, or a citizen intervening in a criminal act.
Essentially, off-duty officers and citizens are both operating with the same disadvantages when they intervene: They are often acting alone in situations which ideally would be handled by more than one person. They are often outnumbered by the subjects they are encountering. They often do not have the equipment necessary to safely intervene - lights, radio, etc. They often haven't had time to pre-plan their response to the encounter.
Pre-planning is a key element, IMO. If at all possible, take a moment, breathe deeply, and decide the best course of action. This doesn't come naturally. It is a learned response which must be practiced. But given practice, this can be an almost instantaneous process.
One of the first things to immediately determine is your role: are you going to be a witness/reporter or intervene? The groundwork for making this decision almost instantaneously should already be in place through your prior mental preparation. The default, IMO, should be witness/reporter if only property is at stake, and intervention, when tactically sound, to protect someone from great bodily harm.
Here's the deal though, you have to consider that everyone you confront is brain-damaged. They aren't in their right mind. You cannot expect them to react in a rational manner. No one drags a woman off into the bushes to rape her expecting to get caught; no one puts a gun to a clerk's face and demands the money expecting to get caught; and, no one starts cutting the catalytic converters of a car expecting to get caught.
When they do get caught by surprise, rational thought processes go out the window. It is a big mistake to expect them to react as a rational person would. Would a person in their right mind stab a store manager to escape getting caught shoplifting a magazine? Hell no, but under the stress of the moment when the only thing standing between getting caught and getting away is the store manager, that happens. It did locally a couple years ago, a fifty dollar misdemeanor beef with no jail time turned into an aggravated battery. Don't tell me the offender was thinking straight.
In too many cases officers come to expect compliance because, well, most folks comply in their experience. You can see how easy it is to develop that mindset when everyone in the last year has been cooperative to your announced presence. Likewise, an armed citizen might expect compliance to their drawn firearm, or threat of a firearm because, well, that's the way they would roll. Remember, under stress, you don't know which way the bad guy is going to roll.
Don't, just don't, expect compliance, and don't intervene when only property is at stake.
JMO, YMMV.