When the little devil has to work, it's a blow (6)
I believe the answer is:
impact
'blow' is the definition.
(thesaurus)
'when the little devil has to work it's a' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'devil' could be 'imp' (devilish creature) and 'imp' is present in the answer.
'a' is present in the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for impact that I've seen before include "The striking of one body against another" , "Forcible contact; marked influence" , "Collision - effect" , "Significance" , "Marked effect; hit" .)