what does "surrounded by muscle"mean?
The men around the coffin decided to adopt Kemp Clark's suggestion; if necessary, they would hold him down. A signal was passed, O'Donnell to Kellerman to the four-to-twelve shift. Rose was surrounded by muscle.

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I suspect that "surrounded by muscle" here means she was surrounded by a lot of gangster/big/muscular type guys. Basically guys with a strong physical presence.