Players in form? (4)
I believe the answer is:
I believe this clue is a double definition.
'players' is the first definition.
(I've seen this before)
'form' is the second definition.
(cast is a kind of form)
'in' acts as a link.
(Other definitions for cast that I've seen before include "protection from injury" , "Throw a fishing line" , "characters together" , "Discard; actors (in play)" , "Throw out line for fish" .)