Wristlocks (known as mao de vaca in Portuguese) are some of the lesser used submissions in Brazilian Jiu-jitsu.
Wrist locks are used widely in Akido, Hapkido and Japanese Ju Jitsu. They are illegal in Judo and Sambo.
They are legal in BJJ from blue belt and upward.
Judo black belt and BJJ brown belt under GiGi Paiva, Ayub Magomadov, demonstrates a nice wrist lock which you can easily use when your opponent wants to break the closed guard by standing up.
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