Book player on bench (7)
I believe the answer is:
reserve
This might be a double definition.
'book' is the first definition.
(as in booking or reserving in advance)
'player on bench' is the second definition.
'reserve' can be an answer for 'player' (I've seen this before). I'm not sure about the 'on bench' bit.
Can you help me to learn more?
(Other definitions for reserve that I've seen before include "Reticence" , "Twelfth man < 's coolness" , "Keep back - book" , "Book - spare player" , "One on bench" .)