Trigger strikes, sharp! (4-5)

I believe the answer is:

kick-start

'trigger' is the definition.

'strikes sharp' is the wordplay.
'strikes' becomes 'kicks' (to kick is to strike with a foot).
'sharp' becomes 'tart' (I've seen this before).
'kicks'+'tart'='KICK-START'

(Other definitions for kick-start that I've seen before include "make a good beginning" , "Activate suddenly" , "Get something going" , "Provide an initial impetus" , "Activate (business or motorbike!)" .)

I've seen this clue in The Guardian.

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