The omoplata (referred to in Judo as ude-garami or sankaku-garami, 三角緘, "triangular entanglement" or ashi-garami, "leg entanglement") is also a commonly featured shoulder lock in Brazilian Jiu-Jitsu. The locking mechanism is similar to the kimura lock, but instead of using a figure-four, it is applied using a leg. The omoplata can be applied from the guard, by placing one leg under the opponent's armpit and turning 180 degrees in the direction of that leg, so that the leg moves over the back of the opponent and entangles the opponent's arm. By controlling the opponent's body and pushing the arm perpendicularly away from the opponents back, pressure can be put on the opponent's shoulder. It is also possible to put pressure on the elbow joint by bending the leg entangling the arm, and twisting it in a specific manner. Though an effective lock, it is more difficult than other armlocks to successfully apply. The technique called a monoplata is a similar armlock that resembles juji gatame or spiderweb position yet has a mechanism like a omoplata.
That clear? Me neither. I am sure he was implying it was illegal in judo. Maybe kids aren't allowed to use it.
Ninjago, as they say.