some normally-built guys can do one-punch knockouts, so how do guys that weigh like 250 pounds of pure fat-free muscle and are like 4-5x stronger than an average guy punch each other in the head without knocking each other out, or even brutal brain damage?
One punch knockouts are rare, in any instance. Firstly, someone who has become an MMA fighter probably has already found out they can stand a few knocks to the head (not a glassjaw). Secondly, MMA fighters are prepared and greased when they get hit, they’re expecting it. At a bar you might not be expecting it, you aren’t a seasoned fighter, and 98% of punches thrown in bars don’t knock people, they just squirm on the ground and moan because they are wusses/not used to it/don’t feel like getting up for another.
WAG
They generally don’t get to take clean shots at each other - they’re skilled fighters so the guy defending the punch will be doing just that, covering up, blocking etc. It has to be very tough to land a clean blow on a skilled pugilist who is actively defending your intentions. MMA fighters wear light gloves, so certainly if a guy were to just hang his chin out there he’d stand an excellent chance of getting KOed. OTOH, MMA fighters don’t wear shoes, so have reduced leverage for throwing punches relative to , say, boxers. You’ve also got the vast range of moves in MMA that makes just standing there and trading blows less of a feature to the game.
Maybe you know this already, but the light gloves plus fearsome power of an MMA fighter is usually seen as a safety feature relative to boxing, which has a far higher incidence of fatalities and brain damage. The big gloves that boxers wear, plus 1 minute breaks every 3 min round, mean that skilled, fit guys can fight for over half an hour absorbing tremendous punishment to the head without getting knocked out. You often see a boxer with a good beard take a full clean shot in his stride - Watch round 1 of Hagler v Hearns for a superb example of this. The cumulative effects are obvious. In MMA, by contrast, a couple of decent blows to the noggin often ends the contest.
In UFC22 Brad Kohler lands a great right cross on Steve Judson’s chin. Judson had his left hand lowered, allowing Kohler a clean shot. Lights out!
I’d wager that nearly all ‘one punch knock-outs’ on the streets come from ‘sucker punches’.
Give me a free, unexpected punch on most men, and if I deliver it right, I’d have a good chance of knocking them out.
Another factor: stronger and thicker neck muscles than the average joe. Knockouts frequently come from shots that whip the head around and cause the brain to impact the inside of the skull, which is why a hook or uppercut to the chin is sometimes called a shot to “the button” that switches the lights off. A stronger neck that keeps the head from whipping around so much equals fewer knockouts. If I got a free shot to the chin of both Brock Lesnar and, say, Andy Dick, I’d be much more likely to knock out Andy Dick because Brock has a neck like a car tire.
Purely coincidentally, this is also the more morally correct course of action. 
Heh.
The gloves make a big difference. They’re more to protect the puncher’s hands than the punchee’s head - punching somebody in the jaw is much more likely to earn you a broken hand than to earn him a broken jaw - but they do cushion blows somewhat.
Second, Hollywood-style one-punch knockouts do not happen in real life, unless you’re talking about blows to the back of the skull.
Third, MMA fighters guard against headshots. That’s why MMA fighters (and boxers) are so quick to jump on a guy who’s had his bell rung slightly - you can do a hundred times more damage with a dozen undefended punches than you can when your opponent has his guard up.
Obviously, no one is speaking from experience. Landing very hard blows that aren’t perfect knockout punches can result in broken fingers/hands/wrists.
The lack of heavy gloving means the puncher can’t (shouldn’t) punch ‘clean through’ his target all the time. It’d be like trying to punch through a wall.
Punching someone clean and punching through them is a major risk. If you don’t knock them out, you might have severely injured yourself in the process.
This is not the only factor, but should be added into the ones already mentioned.
Further, if you have ever punched an crazy, intense, beast of a person, you might be very frightened when you stand there and look at them… as they are not only un-fazed, they seem to ENJOY it.
Slight hijack - having watched a few episodes of the UFC series, it seems like there’s an odd overemphasis on the wrestling aspect - the hitting and kicking that there is seem almost more like when cats bat at you with their paws then serious attempts to inflict hurt. Is this because there are a lot of limitations or rules involved in the fighting? The hitting and kicking parts seem to mostly be half hearted and an after thought compared to the wrestling.
I know NOTHING about fighting, but from a physics standpoint, I’d think the brain would hit the walls of the scull harder if your head moves less. Where as, if your head whips around, your neck will absorb some of the energy before your brain has to.
The problem with striking in MMA is that even if you specialize in it you’re unlikely to get in a knockout blow before your opponent can close, and once you’re grappling or on the ground, all the punching and kicking ability in the world will avail you little.
I’d guess that 2/3+ of each fight is spent locked up or on the mat, so it makes sense to focus 2/3 of your energy on perfecting that aspect of the sport.
By 250 pounds of fat-free muscle you mean 300 pounds of muscle/bone/organ/etc. and 50 pounds of fat? Those guys aren’t even close to single-digit percentage body fat, let alone zero percent.
If you get hit on the head and your head doesn’t move, what is causing the brain to move against the inside of the skull? No energy is being transmitted to the brain if there’s no motion. The punch hits the skull not the brain. The faster the acceleration and deceleration of the head, the more likely you are to have a traumatic brain injury.
That. To punch or kick, you gotta keep a minimum distance between you and your opponent. Once that distance gets closed, the better grappler always wins. That distance is almost always closed, because the “fighting area” is pretty small if I’m not mistaken. And besides, it’s only a quick step between punching distance and grappling distance.
Plus, as any bare knuckle boxer will tell you, it takes quite a bit of work to actually knock out someone with strikes alone. With a decent and fast submission hold, you can end the fight in a few seconds. And not get your teeth knocked out and your face consistently smashed up in the process, which counts as a plus too ;).
Well, I have trained and sparred with some pro MMA fighters. Chuck Liddell punched me in the stomach once.
I don’t know much about MMA or UFC, but my guess is this would be because almost all real fights eventually devolve into fighting on the ground. You set up your opponent with punches and kicks in order to get them off balance so you can throw them to the ground and finish them off. At least that’s what I was taught in Kempo Jitsu. And having seen and participated in my share of bar (and other) fights, this seems to be the way things generally go in real life as well.
As for the OP, I agree with those who say that it has to do with the preparation of the fighters, and the fact that in real life you rarely see anyone knocked out with one punch. In my own fighting experience I’ve seen a person knocked out exactly once with a single blow…and that was with a fluke round house kick that caught the guy on the side of the head and hurled him into a wall. I’m not sure if it was the kick or the wall that knocked the guy out…
-XT
Right. It’s kind of like when your parachute doesn’t open - the fall isn’t so bad, but the sudden deceleration is a bitch.
I think it’s clear the poster meant “250lb guys who are showing all their muscles.”
An extended family member likes to mention how he once pinned Chuck Liddell. When they were 16, in HS, of course.
Then you have Liddell, who simply refuses to wrestle with you. He uses his wrestling/grappling practice to stand up as quickly as possible. I’ve been amazed at how fast he’s been able to get to one knee and then get a foot under him. He’s willing to let you punch him, hold his arms pinned, take his back, as long as he can stand up.
As for that “drop like he’s been shot” punch, is it possible that some of them are due to hitting key nerves? I thought I heard that many years ago. I mean, Fedor dropped Arlovski like a sack of wet meal. I’ve seen guys get knocked about clean off their feet and retain most of their senses. I almost guarantee you Arlovski’s been hit that hard in most of his fights. I’ve been replaying it over and over just now, and he gets hit on the side of the jaw, and his head doesn’t even move that much.