When I was in grade school I had a classmate who was really good at Judo. Her name was Renee Hock, and she went to national competitions and everything. I don't know if she ever made it to the Olympics but she has a page on JudoInside. and the Internet says she's a black belt now. She went to the world championships and the Pan Am Games, where she won a bronze medal, apparently.
And while we were all very supportive of her efforts, none of us ever had any idea how judo worked. We always joked about doing "the Crane" like the Karate Kid, and I'm pretty sure she hated us for it.
Chances are, even now, you still don't know how judo works. It's one of the world's oldest sports, but even if you were transfixed in front of your television Tuesday watching Antoine Valois-Fortier win a surprise bronze medal, chances are you're not exactly sure how he did it.
It's not like Canada doesn't have a history with judo. Valois-Fortier's coach, Nicholas Gill, won silver in 2000. Gill also won bronze in 1992. Considering Canada's medicore summer Olympics track record, judo probably pops up as often as anything else not named Ben Johnson. But it's like the modern pentathlon: we don't understand it, but we like cheering for our people when it's on TV.
Part of the mystery of martial arts is in the nuance. Where taekwondo is aimed more at strong, assertive defence of your person, judo leans more towards continuous offensive manoeuvres. The goal is to get your opponent on their back, but in a strong, swift move that asserts authority. Points are handed out for full completion of a scoring move, as well as partial scores for other moves.
The scoring goes as follows:
-Ippon: a fill throw, with speed and force, where the opponent lands fully on their back. A successful Ippon ends a match. An Ippon also applies if you can flatten your opponent for 25 seconds, choke out your opponent, or dislocate their arm. Seriously.
-Waza-ari: this is a half-point, awarded for an Ippon-like move that lacks force or that doesn't result in the opponent landing on their back. You can also get a half-point if you immobilize your opponent for over 20 seconds (but less than 25).
-Yuko: a quarter-point given for a move where the opponent lands on his back, or is thrown on his side with speed or force (but not both).
Penalties work much like hockey penalties. A first penalty (a "shido") gets a warning, and for each ensuing shido, you get a "shido" for which your opponent gets a yoku. In other words, you give your opponent points every time you cheat.
Now for the tricky part: two waza-aris equals an ippon, but yukos can't be added together to get a waza-ari. However, if you get more than one shido, the penalties are progessive; four violations and you lose the match.
You can also combine your score and the opponent's penalties to get a win. If your opponent has three shidos and you score a waza-ari, you win, for example.
In summary: first point wins, except scoring is done in half and quarter points, and half-points can be added to equal a full point, but quarter points can't be added to equal a half-point, unless you get a penalty that gives your opponent a quarter point, in which case they can all be added to equal a full point.
Unless your arm gets dislocated.
It's all very complicated and cerebral - which is probably why Canadians are good at it.