The Knockout is not a Chaplin short per se. It is also not a knockout by any means.
It’s primarily a vehicle for Roscoe Arbuckle. He plays “Pug,” a genial sort who, for reasons I still haven’t sorted out even after seeing the movie, gets talked into a boxing match against a prizefighter named Cyclone Flynn (Edgar Kennedy).
Chaplin has a very brief role as the fight’s referee. The running gag of Chaplin’s appearance is that, by being in the middle of the fight, he endures the brunt of the punches. Mild as that sounds, it’s probably the funniest thing in the movie.
The movie’s finale involves the Keystone Kops and makes even less sense. Chaplin would work the boxing ring himself to far greater effect years down the road, in City Lights (1931).