Strike back at the friends (4)

I believe the answer is:

slap

I'm a little stuck... Click here to teach me more about this clue!

'strike' is the definition.
(I know that slap is a more specific form of the action strike)

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

Can you help me to learn more?

(Other definitions for slap that I've seen before include "Cuff" , "Hit with an open hand" , "Make-up (slang)" , "Mild punishment" , "Strike action" .)

I've seen this clue in the Evening Standard.

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