Amateur team having ace in reserve (3,5)
I believe the answer is:
lay aside
'reserve' is the definition.
(I've seen this before)
'amateur team having ace' is the wordplay.
I cannot quite see how this works, but
'amateur' could be 'lay' (similar in meaning) and 'lay' is found within the answer.
'team' could be 'side' (both can mean a sports team) and 'side' is found in the answer.
'ace' could be 'a' (abbreviation) and 'a' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for lay aside that I've seen before include "Abandon - store for future" , "Abandon - save for later" , "reserve" , "give up!" , "Discard - put by for future use" .)