It's handy when your foot's half dead! (4)
I believe the answer is:
deft
'it's handy' is the definition.
(I've seen this in another clue)
'your foot's half dead' is the wordplay.
I cannot quite understand how this works, but
'dead' could be 'd' (abbreviation in government records) and 'd' is present in the answer.
'foot' could be 'ft' (abbreviation) and 'ft' is found within the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'when' is the link.
Can you help me to learn more?
(Other definitions for deft that I've seen before include "Adept" , "Handling things skilfully or neatly" , "Adroit, dexterous" , "Quick and skilful in movement" , "Quick and dexterous" .)