“A Knockout” comes from Cuphead, the 2017 run-and-gun game by Studio MDHR, where a vintage-style announcer calls out major fight moments. The line became popular beyond the game because its short length and dramatic delivery fit edits perfectly. It spread through gaming clips, meme compilations, and reaction videos as a quick way to signal a total win. It still gets used because the phrase is simple, recognizable, and pairs naturally with boss fights, speedruns, and sudden turnarounds.