It’s probably worth stressing again: there is no such thing as safe
violence. You can try to mitigate the harm done, but you can’t negate it entirely. When you’re
looking at a situation and saying you need a solution that ends without
anyone getting hurt, the only ones which can guarantee that are
non-violent. If you’re resorting to violence, it has to be with the understanding that harm is an acceptable outcome. As someone with “considerable”
combat experience, your character would know and understand that.
Note that, I said “acceptable,” not “desired.” You can get a lot of
mileage out of someone who wants to deescalate the situation, doesn’t
want to hurt their opponent, but is running out of non-violent options. The final duel in Return of the Jedi is a classic example of this playing out.
Responsible hand to hand combat is (usually) about balancing the amount of force you need to achieve your objectives, without harming your opponent(s) excessively. Unfortunately when your goal is to incapacitate, that’s going to require a lot of harm. This is also why you’ll see actual martial artists try to defuse the situation rather than resorting violence. It is the safest way to achieve their goals (of not having everything pear-shaped around them).
With that said, joint locks and submission holds come to mind. Unfortunately, this probably isn’t the solution you were hoping for, because it means you can’t just wander off, you need to stay there, physically holding your opponent in place. If your character wants to try to talk their opponent down, these do allow for the attempt, but it’s still better to start with talking, and only resort to locks when persuasion fails.
Locks work by manipulating your opponent’s body into a position it can’t escape from. Twisting the arm up behind the back is a classic example, you’ve probably seen in film and TV. This is mostly because it’s a very easy lock to fake for the camera. But, there are a lot of joint locks (particularly ones that start with the wrist) that can completely immobilize a foe from basic counters.
If you just need to hold someone in place to buy time for reinforcements or the police, then this is the ideal solution. Honestly, generally speaking, this is the best option in a self defense situation, when it’s viable.
Even then, this isn’t harmless. In a controlled environment, locks and holds can be practiced safely. But, if your opponent struggles against the more effective holds, and refuses to submit, they can seriously injure themselves. Also, if you misjudge the hold, it is possible to lose control. These are temporary solutions at best, not permanent ones.
If you need your character to stay mobile, that’s not an option. If their opponent is just an obstacle, they need to get around, then simply bolting past may be the best option.
If they need to immobilize their opponent, and stopping him is the priority, then one good option is restraints. These aren’t harmless, or foolproof, but it sets a good balance for neutralizing them without adding unnecessary force.
Zip tie restraints are pretty cheap, disposable, and allow you to “tie someone up” in a matter of seconds. Depending on the style, you can get them for less than $2 a unit, meaning even if they’re on a budget, your character can probably afford a few. They’re also fairly secure, unless you know what you’re doing, most people cannot get out of these on their own.
If you need something a little more secure, police handcuffs are going to cost, but unless you’re dealing with police, or an escape artist, getting out of these is probably not happening. Of course, they’re also a lot more expensive, so just leaving someone in cuffs is probably not happening, unless they’re very well funded.
Still, your best option is probably to try to talk it out, and, if need be, bolt. Or accept that if violence is necessary, someone’s going to get hurt.