Crossword Genius

Threat of force — Spooner's spray didn't work (6,4)

Ross

I believe the answer is:

mailed fist

'threat of force' is the definition.
(mailed fist means a threatening display of force)

I don't understand how the remainder of the clue works.

(Another definition for mailed fist that I've seen is " military force".)

I've seen this clue in The Guardian.
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