First, the science:
https://rollingaroundbjj.com/fights-end-up-on-ground/
That article looked at 383 street fights which were available on Youtube. Never mind the fact that in order to make it onto Youtube in the first place, maybe something spectacular had to happen, or maybe it was just a stupid looking fight. Who knows. So the data set might be a tad skewed. Still, with just Youtube to go by, the results are shown in the article.
They concluded:
Summary:
- Most fights start with someone who’s unprepared getting punched in the face… even though there‘s lots of indicators it’s about to happen.
- The aggressor then gains the initiative with a flurry of punches… and often wins within seconds.
- Most losses were a result of not having a basic boxing protective stance or guard… and getting hit in the face by an unskilled opponent.
- Less than 1/3 of fights end up on the ground in a way that grappling would be useful.
- When used, takedowns were one of the most effective street fighting techniques because they either end the fight or put you in a dominant position.
- Grappling styles like Brazilian Jiu Jitsu are very effective in street fights… especially for gaining and maintaining a dominant position.
- Multiple attackers are more likely to be an issue if you are in a striking-only fight and get knocked down.
And for the record, I agreed with the conclusions of the article. It jibed with what I've concluded on my own after watching Youtube videos and a small number of real life fights.
The main thing I'll observe as it pertains to this question is that it's not that you're going to encounter a particular technique the most. That's not what you should concern yourself most with. Instead, it's the attitude, for lack of a better word. Yours and theirs.
If you watch some Youtube videos of street fights, you're going to start seeing a pattern. The pattern is that the guy that looks unwilling to engage is going to get hit first and will probably lose. He's an easy target, because he simply doesn't want to fight and isn't mentally prepared for it. Mentally, he's not in the game. He has already lost the fight in his head.
This typically takes two forms. First is the guy who's posturing up, sticking his chest out and stepping towards the other guy. He's the aggressor. The other guy takes a step back, looks around, looks down, and often tries to avoid eye contact. He's using his voice and body language to indicate that he does not want to fight. He's backing down before anything happens. And in his head, he has no intention of fighting. Then the first guy throws a punch at his face, and it connects. After that, there's not enough time for the defender to switch "on" mentally in order to have a fighting mentality. He loses easily.
The second form is where you have a loud mouth guy who gets up into another guy's face screaming and generally trying to make the other guy back down. After a while of this with no strikes thrown, the guy who simply stood there and did nothing throws the first strike and knocks the loud mouth down. This seems like the exact opposite situation as the first one, but what's common is that the ones that lost the fight were the ones that proved from the very beginning that they did not want to fight. By spending a lot of time yelling and posturing instead of throwing a punch or even just shoving, the loud mouth guy indicates to his opponent that he doesn't intend to fight for real. If he did, he would have already done so. The other guy merely stood there unflinching, mentally preparing himself to strike when he saw the opportunity. And he took it.
The key appears to be attitude. If you show you're unwilling to fight, the other person will realize it on some level and may throw the first punch. It's like there's a switch you have to turn on in your mind that says you're fighting, and there's no backing down from this point on. It's a fight.
And while the winner generally is the one that throws the first punch, you don't have to be that guy in order to win the fight. You just have to be ready for his first punch. By the time it starts, you need to have yourself mentally prepared for it. You'll lose otherwise. You may still lose even if you're mentally prepared, but you will definitely lose if you're not.
Getting back to the technique, again that is far less important than what's going on in your head and what you're telling your opponent with your voice and body language. The fight is over already before it begins unless you're on top of it mentally. But what about the techniques you're likely to encounter?
The answer is that you're going to get mostly the same sorts of techniques thrown at you in the first moments of the fight: Guy looks away, pauses for a second, and then turns and immediately throws a haymaker punch at your head. Guy starts shoving you on the chest and pushes you back, sees that you're not retaliating, and then punches you in the face. Guy puts his hands up in a boxing guard and begins to dance around, sees you're not defending yourself, and then throws a bunch of strikes to your face, following up with strikes as you're falling to the ground. Guy grabs your shirt and wads it up in his fist as he tries an overhand right to your nose.
There won't be a lot of body shots. There won't be a lot of kicks or grappling. In the first moments of the fight, it's going to be mostly punches aimed at your head for a knock-out. I've seen some headbutts, too.
Which is why the article above concluded that one of the worst things you can do as a defender is to not know basic boxing technique. You have to guard your head. You have to be able to switch it on immediately. You have to be able to read your opponent and time it. You'll need to be mobile and ready to move, ready especially to move your head, because that's their primary target.
What happens after those first few moments of the fight is anything goes. It could devolve into a wrestling contest. Ladies like to grab each others hair. Sometimes you'll see kicks, especially if someone falls down to the ground. Etc.
But the most important thing is what happens before the first punch is thrown. That's what determines who wins and who loses, generally. You have to be prepared for it on a mental level. If you're not, that punch will land on you. And you'll just be dazed and confused. You won't know what's happening. And when you're not defending yourself, he's just going to take advantage of that and throw a flurry of strikes at you. All of them will connect. And one is going to knock you out.
Hope that helps.