Kazotsky Kick

Short answer: 'Kazotsky Kick' is the name of a group taunt in Valve's game Team Fortress 2. It was added on July 2, 2015, in the Gun Mettle Update.

Any class can perform it, and other players can join in. The official TF2 Wiki calls it a hopak set to a fast folk tune, with variations for each class. The step itself is the prisyadka (also spelled prysiadka), a squat step in which the dancer drops onto the balls of the feet and kicks the legs out one at a time while keeping the back straight. The squat-kick step comes from folk dance of the former Russian Empire and Soviet Union, including the Russian prisyadka and the Ukrainian hopak; the game wiki calls the taunt a hopak. Britannica traces the hopak to the Zaporozhian Cossacks and describes improvised leaps, squatting kicks and turns, and Dictionary.com calls the prisiadka the signature step of the kazachok, a Cossack-style dance. The name 'Kazotsky' isn't a traditional dance name; it's best known from the game. The footage shows men in Soviet-style military uniforms doing squat kicks in what appears to be a colorized archival film. The source doesn't identify the clip, so the case doesn't either.