Conflict, crime and law

Black market

Where goods are illegally bought and sold for profit.

Blackball

Exclude or ostracise someone socially; reject someone.

Blacklist

Exclude someone.

Blackmail

Extort or take money from someone by threatening to use their secrets against them.

Catch someone red-handed

Catch someone in the act of committing a crime or doing something they shouldn't.

Do time (serve time)

Spend time in prison.

Hold the fort

Have responsibility for something or care about someone while others are away or out.

Long arm of the law

Far-reaching power of the authorities.

Red flag

Signal or indication that something is not working properly or correctly.

Shown the red card

Dismissed or told to leave.

Standing ground

Maintaining your position.