In reserve team after Adrian's debut (5)
I believe the answer is:
'in reserve' is the definition.
(I've seen this before)
'team after adrian's debut' is the wordplay.
'team' becomes 'side' (I've seen this before).
'after' means one lot of letters go next to another.
'debut' indicates taking the first letters.
The initial letter of 'adrian' is 'a'.
'side' after 'a' is 'ASIDE'.
(Other definitions for aside that I've seen before include "Whispered comment" , "Away from main action" , "Remark not for hearing" , "kept in reserve" , "(Pushed) out of the way" .)