Green’s Dictionary of Slang

sandbag v.1

[i.e. to hit with a SE sandbag]

1. [late 19C+] to ambush, to take by surprise.

2. [late 19C+] to cheat, to trick.

3. [20C+] to get rid of.

4. [1920s+] (US) to intimidate.

5. [1930s] to extort.

In compounds

sandbag artist (n.)

an extortionist.