Hot answers tagged teaching
Capoeira! Well, just kidding. I think some big guy's grappling would suite him. Sambo, Greco-Wrestling, Judo... or maybe Keysi. Keysi seems pretty practical, and does not involve much kicks. Fit for brutes. but footwork from boxing might help him be faster.
He already has a great grappling foundation from what you've posted. I would think about going with a defensive martial art like jujutsu (traditional rather than brazilian). It will teach him enough defense to protect against low blows that are his weakness as well as how to get in close to the opponent so he can use his size to his best advantage. Also, ...
Wrestling, Judo or BJJ are good options because 1) he's strong and 2) he's big, so it will be difficult to perform locks on him unless you have VERY long arms. He may also benefit from a bit of boxing so that he can learn to punch faster.
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