Gennady Golovkin boxes.
Gennady Golovkin . With a streak of 23 knockouts that spanned from 22 November 2008 to 18 March 2017 , he holds the highest knockout percentage -- 89.8 % -- in middleweight championship history . A knockout ( abbreviated to KO or K.O. ) is a fight-ending , winning criterion in several full-contact combat sports , such as boxing , kickboxing , muay thai , mixed martial arts , karate , some forms of taekwondo and other sports involving striking .