Save the substitute (7)
I believe the answer is:
reserve
This clue is a double definition.
'save' is the first definition.
(I've seen this before)
'the substitute' is the second definition.
(synonyms)
(Other definitions for reserve that I've seen before include "Twelfth man < 's coolness" , "Reticence" , "Lack of openness" , "One on bench" , "ice" .)