It’s a reference to Wagner—an openly Neo-Nazi Russian outfit—use of the sledge hammer on innocent people on video tape.
First of a Syrian alleged deserter, who was tortured on video by having his hands and feet smashed with a sledge hammer. Then they cut his throat, removed his head, hangs and feet, and hung his body up while posing next to it.
The second is of a prisoner who was returned into their custody and then executed with a sledgehammer because he did a video for Ukraine where he stated he didn’t really want to be there and offered to join the Ukrainian side.
I guess that’s technically “gangster,” in the sense of being criminal and pure evil.