Shows a yellow card to rugby players hiding ball (5)
I believe the answer is:
books
'shows a yellow card to' is the definition.
(as in a referee booking footballers)
'rugby players hiding ball' is the wordplay.
'rugby players' becomes 'boks' (Springboks, the South African rugby team).
'hiding' is an insertion indicator.
'ball' becomes 'o' (O looks like a ball).
'boks' enclosing 'o' is 'BOOKS'.
(Other definitions for books that I've seen before include "Reserve tickets" , "See 1" , "Reserves" , "Tomes, volumes" .)