Surprise is absolutely critical; the rest, not so much.
Here’s the thing, if your untrained combatant is the aggressor, then they’ll need to hit the trained martial artist with overwhelming force before the martial artist can respond. Full stop.
The “before the martial artist can respond” part, is where we get into the surprise range. If your untrained combatant can’t end the fight with the first strike, then the situation will go badly for them.
I should probably point out, what I’m calling a “martial artist” here is ridiculously broad. This isn’t just formal schools, I’m lumping in just about anyone who’s undergone basic hand to hand training here.
When I’m saying “untrained”, I’m actually excluding street fighters, and people who have a fair amount of hand to hand experience but little formal training. They’re an edge case that doesn’t follow the rules consistently.
Untrained combatants tend to fight very predictably, and any martial artist who’s gone through even basic self defense, will have been taught to counter most of an untrained fighter’s repertoire.
An untrained fighter can’t do a lot of damage with a sucker punch. Certainly not enough to incapacitate a trained combatant. The opposite is not true, a trained martial artist, particularly from Karate, can use a sucker punch as a takedown strike against someone who hasn’t been conditioned to tense their abdominal muscles before a hit.
Getting a combatant angry can have one of two results, and again, we’re back to the trained/untrained thing. An untrained combatant will start to lose control (usually) when angry (making them less dangerous). A trained combatant will usually get more brutal.
Here’s a thing worth pointing out, most conventional self defense, and even a lot of non-military training, like police hand to hand, places a premium on the safety of both combatants. Angering a combatant trained in any of these forms (and this includes most martial artists trained as recreation, who’ve had some self defense classes splashed over their training), will at best cause them to start striking more brutally, and with less concern for their opponent’s well-being.
When you’re talking about drugs, I’m going to go out on a limb and assume you mean things like PCP, not, say, mescaline. Because if your untrained combatant is tripping balls… it’s funny, but they’re not really that dangerous to a trained combatant.
Things like PCP, where pain response is deadened, and even some fugue rage state change the rules a little, but not enough. Your untrained combatant is going to be sacrificing efficacy for a little more durability… but, here’s the thing, it won’t really help them.
Depending on what your martial artist has been trained in, someone under the influence of PCP can be a legitimate threat. Akido, Judo, and Jujitsu, fighters wouldn’t face any real threat from someone on PCP, while someone trained in Karate (because of the way it’s joint locks work) could be in serious trouble.
Most trained fighters, when confronted with someone on PCP should know enough to break away and get out of the fight. And that actually goes for some circumstances that could apply elsewhere. I was being snarky earlier, but a martial artist, when presented with a firearm, should know enough to get the hell out of there before they get shot.
You’ll have a great deal of trouble taking a trained combatant by surprise from a face to face assault, especially if you attempt to sucker-punch to the face or even just the stomach or the groin. This is because they’re eyes and body have already been trained to watch for strikes, they’ll see the motion beginning in someone else’s body and sucker-punches are heavily telegraphed.
If you do connect, they better go down on the first blow. This is hard, especially since for most martial artists and trained combatants the first strike acts more like a wake-up call and their brain and body go: “oh! okay! I’m here!” If you can get them with a knife before they know what’s happening great, the same goes for a taser or a cattle prod.
If they’re the aggressor, then they already have an objective, they already know what they’re going after, and without help, your character won’t be able to regain control of the fight.
For a trained combatant, surprise and anger just trip the brain over into a more focused place. They feel the rush of the adrenaline and they settle, the world becomes clearer, then they act. They’ll do this in any panicked situation. This isn’t true for untrained combatants, they tend to lock up in a fear response, anger makes them lose control and they become less dangerous.
You might be able to get a trained combatant from behind, but even this is hard. Martial artists tend to be very aware of anyone entering their personal space, even from behind. I once had a moment with my now ex-boyfriend in high school where he came in for a hug from behind and he surprised me, so I elbowed him in the gut. It was an automatic response. He hadn’t even touched me yet, but it happened anyway.
A combatant has been trained for their body to respond automatically, they train against other people who have also been trained, and I’ll be honest, watching an untrained combatant is like looking at someone fighting in slow-motion. It’s a strange, surreal experience for me.
It’s also important to point out that most of the aggressive “jock” responses you get from untrained male combatants, aren’t what you get from trained ones. The over-aggression comes from insecurity, like any bully, but usually a martial artist knows what they are doing, how to do it, and are confident and secure in their ability to protect themselves. They don’t need to prove their mettle in a fight because they’ve already proven it to themselves.
This is an important tell, by the way, in a character noticing the difference between someone who knows what they are doing and someone who doesn’t.
I think we’ve covered the bases here. I hope that answers the question.