Exposed groups of players, those regarded as rejects (8)
I believe the answer is:
outcasts
'those regarded as rejects' is the definition.
'exposed groups of players' is the wordplay.
'exposed' becomes 'out' (I've seen this in other clues).
'groups of players' becomes 'casts' (groups of actors).
'out'+'casts'='OUTCASTS'
(Other definitions for outcasts that I've seen before include "People rejected by society" , "Pariahs" .)