Contract only an upper projection when off-duty (2,5)
I believe the answer is:
on leave
'off-duty' is the definition.
(I've seen this in another clue)
'contract only an upper projection' is the wordplay.
'contract' means to remove the last letter (contract can mean to shorten).
'an upper projection' becomes 'eave' (I've seen this in another clue. I am not sure about the 'upper' bit.).
'only' with its last letter taken away is 'onl'.
'onl'+'eave'='ON LEAVE'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for on leave that I've seen before include "Currently away from work" , "Not required for work" , "Having an official holiday from work" , "Holidaying" , "absent from work" .)