Five Knuckle Shuffle

Does anyone know what the [British] term "Five knucle shuffle" means? I saw it on an Amazon.com review by a London viewer.

Slang for male masturbation as per a few websites.

www.well.com/ user/earl/synonyms.html

Based on context, of "They got into..." there is no way it could be refering to masturbation. A fist fight seems to fight nicely.