Reserve men on board enjoying quoits? (4)
I believe the answer is:
book
'reserve' is the definition.
(booking is a kind of reserving)
I don't understand the rest of the clue.
(Other definitions for book that I've seen before include "Volume - maybe thrown at offender" , "Bound volume" , "Leaves, bound" , "Reserve - publication" , "Reserve - something to read" .)