I think this short story was in one of the “Gold” collection series.
It was about the murder of a Martian who played a form of golf using a jewelled boomerang. The human eventually convicted ends up in an execution chamber designed to execute Martians, who have a hard carapace.
It would have been a contemporary of such favourites as “Watchbird” and “Horror Howse” (yup, that’s how it was spelled, as I recall). I’m looking for the title, author and collection title.
Are you sure it was Mars and not Venus?
Otherwise it sounds very like Fred Pohl's "The Gentlest Unpeople". The central character, an explorer from Earth iirc, has accidentally killed a Venusian in the middle of a "whirlarang" contest. The Venusians accept that the killing was accidental, but he has nonetheless incurred the death penalty by interrupting the game.
Executions are performed by a robot which apparently just tears the offender to pieces. As a kindness, he is led to believe that he is being reprieved, but then taken into a room where the Justice Machine awaits him.
The story was indeed included in The Fourth Galaxy Reader, edited by Gold.
