The easiest mistake to make when going to the World Jiu-Jitsu Children's Cup would be to assume the event would be a nice, quiet easing into the main business of this event - the Abu Dhabi World Professional Jiu-Jitsu Championship, which begin today.
Children competing in what is the most passive martial art, an art far more about defence than attack? How intense is that going to be?
Well, quite seriously intense, actually.
Around midday, one competitor, no more than 12 years old, huffed off the mat after a tight loss and did so with such intent that his father (and coach) tried but failed to stop him stomping off back to the players' area.
They kept asking him: "Why are you so angry?"
Later, another father spent 15 minutes engaged in - let us call it an enthusiastic and extremely technical - discussion with a referee after his son had actually won. The discussion was about one specific move.
It moved the referee to smile afterwards and remark: "Nope, this isn't child's play."
It is not as if, however, that this was a convention of pushy tennis parents. There is none of the creepiness, the scary narrow focus on victory alone: the very nature of jiu-jitsu precludes that.
Nearly 650 children, including 50 invited from around the globe, took part but in truth the participation was far greater, spread out to include their parents, wider families, friends and coaches.
"Always I am in there inside with him," says Alan Fontanella of his son Enzo, coaching, sympathising and feeling it from the sidelines of the mat.
Fontanella, a Brazilian pilot based now in Dubai, is himself an enthusiastic jiu-jitsu fighter, continuing a family tradition.
"In Brazil, when you are born, if you are a girl you do ballet, if you are a boy, you do jiu-jitsu," he says.
Abdullah Al Nyadi has no background in any kind of martial arts, though he dearly wanted to when he was growing up.
He is happy his two daughters Hajra, 15, and Maitha, 13, (and a son, Hamdan) were all taking part, and winning, yesterday.
His children are the fruits of the UAE Jiu-Jitsu Federation's push of the sport at school level and are a fairly remarkable bunch.
This is the first year schoolgirls are competing. Hajra and Maitha started with karate and have done wrestling and kung fu and now train with the federation.
"I had an interest and wanted to learn but back then there was nothing," Al Nyadi says.
"Now I saw they had a chance, I introduced them to it and they liked it. It has helped them a lot because in martial arts the first thing it teaches you is self-confidence, then discipline and then self-defence."
His friends, he says, are often surprised at his daughters' pursuits, but the message is spreading.
"I was discussing it with one yesterday and they want their daughters to get into it, as well, now. These days, I feel it is necessary to do something like this."
Takamasa Watanabe is here, like many others, in a dual capacity. He is the director of the Japan Jiu-Jitsu Federation, and has brought over a delegation of 23 competitors, including 10 children between the ages of 12 and 15. One of the children is his son, 14-year-old Tetsuya.
"I do get nervous watching him but I try not to show it," says Wantanabe.
"He has been training for six years now but this is his first time here. His mother stays the coolest out of all of us when he competes."
The most resounding affirmation, however, of just how important - and serious and intense - the children's cup is comes from Mixed Martial Arts (MMA) and the UFC legend BJ Penn.
The Hawaiian is in Abu Dhabi as a guest through the tournament and was a jiu-jitsu legend in his own right (best known for being the first non-Brazilian to win a world title, in 2000) before switching.
"If this was here, a tournament like this, when I was young, maybe I would never have gone into MMA and UFC."