For the under eleven, diminish (7)
I believe the answer is:
subside
'diminish' is the definition.
(I've seen this before)
'for the under eleven' is the wordplay.
I cannot really understand how this works, but
'under' could be 'sub' (I've seen this before) and 'sub' is located in the answer.
'eleven' could be 'side' (a football side) and 'side' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for subside that I've seen before include "Abate" , "Diminish" , "Sink, settle" , "Wane" , "Cave in" .)