Thanks for the A2A. (This is written in the context of the film, from a martial arts perspective, it isn’t meant to have any opinion on the viability of techniques or approaches in real life).
There are a couple of reasons for this, one is quite obvious, the other is a lot more subtle.
Obvious reason:
He lost and he knew it.
As the tournament progressed, it became apparent to John Kreese, who for all his failings is an experienced fighter and tournament coach, that Daniel was far better than he thought he was. He completely underestimated the teachings of the “old man†and his traditional ways. He made a few tactical errors:
Tactical Error 1: He failed to research his opponent. Not Daniel LaRusso, but Nariyoshi Miyagi.
Sun Tzu famously said in The Art Of War: “If you know the enemy and know yourself, you need not fear the outcome of a hundred battles.†[1]
So let’s think about this for a moment. You have your students, one of which is a star fighter with at least one championship to his name, who are picking on another student at their school. They follow him, attack him, and all three are dismantled by an old handyman.
Then this handyman brings his young friend into your dojo, asks you to “leave boy alone†and then you challenge him to fight in the biggest upcoming tournament in the region. This old handyman doesn’t bat an eye and agrees, saying he will train the boy. Then walks out. Of your dojo. Full of trained fighters. And doesn’t give a single care about it.
And Kreese just lets this happen?
He messed up, badly.
Had it been me in his place, I would have been immediately wary about this entire thing. Three top students, including a champion, in the prime of youth got beat down by an old man and then he agrees to train our target with barely a shrug? Nope, something is going on here. I would have immediately started research, it’s easy enough to find out where LaRusso lives, it’s where the kids jump him. You have a secretary or something start doing research on who may be associated with that place. Then you find out there’s an old Okinawan man there as a handyman? Name of Nariyoshi Miyagi? Hmmm…
And I start making inquires. This was pre-internet and therefore pre-Google, but John Kreese is a connected and influential man. I get on the phone and start calling around, my first call going right to Terry Silver, my old Vietnam buddy and current multimillionaire/billionaire businessman. “Hey man, this and this happened, name’s Nariyoshi Miyagi, can you find out more. Thanks. Cobra Kai; Never Die.â€
Being a former green barret as Kreese was, I would have then requested military records. And what would have come back?
“Nariyohi Miyagi; Medal of Honor recipient, member of the legendary 442nd Infantry, was also awarded the Silver Star, Bronze Star, Army Commendation Medal, Purple Heart and World War II Victory Medal.†Okay…. then after more digging, you find out he trained his commanding officer, Lt. Jack Pierce, karate, who would later go on to be a hand-to-hand combat instructor and curriculum author for the U.S. Special Forces.
Oh, fuck…
Terry Silver comes back with pretty much the same information, except he finds out that he comes from a small village in Okinawa, which is now dominated by a local businessman by the name of Sato. Who owns a prominent dojo on the island. Terry made some calls to some U.S. Military contacts on base there, who train at the dojo (as shown in Karate Kid 2) and apparently Sato learned it from some old man on the island “back in the day.†Name of…Miyagi.
Oh, double fuck.
I immediately go into caution mode. I assign the “normal†students to an assistant sensei (who isn’t Johnny Lawrence) and concentrate on one-on-one instruction for my tournament competitors, especially Johnny Lawrence. I throw kata out the window, anything like that. No more hard-sparring to reduce injury, all medium sparring, drill work. A real focus on the fundamentals, because this could be bad. This is a war hero who bleeds bravery who grew up in a karate family, in a rough area, who is training one single kid; every day.
Which leads us to his second mistake.
Tactical Error Number 2: He failed to take into account what one-on-one focused training can do.
John Kreese continued to train his entire dojo, presumably. Standard times, standard classes, maybe more intensity because of the upcoming tournament. But still, the entire class.
Meanwhile, this freaking veteran murder machine is training a hungry poor kid (hello, Duran, Dempsy, Tyson, Frazier, etc, all from less fortunate beginnings, all hungry. the movie Rocky is based on this concept) who is desperate, angry and scared. And he’s training him one-on-one, every day, for hours per day.
John Kreese simply didn’t take into account how quickly that kind of training can advance someone. One on one coaching, with that frequency, can really bring along someone quickly. He made a mistake, he underestimated the entire situation, and as a result; he lost.
In the tournament he could see it, not just as Daniel fought against his boys, but against students of other dojos. He was better trained and better prepared than he ever thought possible. He represented a clear threat to his tournament dominance. And LaRusso wanted it, badly. He had drive. The, uh, “eye of the tiger†to borrow an idea.
By the second round of the tournament John Kreese saw all of this, he saw he screwed it up, and was willing to do whatever it took for his students to win, by any means necessary. It was no longer important just to look dominant, to look good, the only thing important was survival. Walking out of that building with the championship. How that was accomplished didn’t matter at that point.
Hence; “the knee†and “sweep the legâ€.
He lost, he knew, he wanted to win. So fight dirty.
However, the second reason is quite a bit more subtle.
Because he wanted to hurt LaRusso
John Kreese didn’t like Daniel LaRusso, didn’t like him the moment he laid eyes on him when he walked into his dojo, asking for help with the bullies he produced. He considered LaRusso weak, a bit pathetic, and just everything he spoke out against in this dojo’s doctrine.
Beyond that, he didn’t like the “old manâ€. There is a reasonable chance that John Kreese is a racist against Asians, some Vietnam vets were and I think this was a subtle undertone in the movie. So he didn’t like Miyagi-sensei as a matter of course. He didn’t like what Miyagi did to his students; one; he interfered and two; he won. There’s something about Miyagi-sensei’s quiet manner that disturbs him.
I think on some level, Kreese looks at Miyagi as everything wrong with “traditional†karate, it’s lack of aggression, it’s serenity, all of that goes against everything that Kreese believes as a “warriorâ€. For Kreese, karate isn’t about defense, it’s about aggression in the face of obstacles.
“We do not train to be merciful here. Mercy is for the weak. Here, in the streets, in competition. A man confronts you, he is the enemy. An enemy deserves no mercy.â€
-John Kreese, Cobra Kai sensei
[which isn’t entirely incorrect, but we’ll leave the real-life analysis of the various philosophies out of this answer. Real-life is many shades a grey, things are more subtle than portrayed in the movie]
Where Miyagi-sensei instructs that karate is for defense, to do what is necessary to survive. The goal is to not fight.
In this, John Kreese can’t stand the opposing viewpoint, and as a consequence wants to show his “men†how the “no mercy†thing actually works. And the best way to do that is to have them hurt Daniel LaRusso in the tournament. That way they will emotionally confront the personal ramifications of injuring an opponent, as well as teach them to do “what must be doneâ€. As a bonus, he gets to destroy a kid he doesn’t like, an old man’s emotional state, and a philosophy all in one fell swoop.
Winning dirty would serve two purposes; it would preserve the championship when he was going to lose it and it would exemplify “no mercyâ€.
But that didn’t work either, and because of this; he was a failure.
