Reassert case over including player (7)
I believe the answer is:
actress
'player' is the definition.
(actress is a kind of player)
'reassert case over including' is the wordplay.
'including' indicates the answer is hidden within the clue.
'over' says the letters should be written in reverse.
'ssertca' can be found hidden inside 'reassert case'.
'ssertca' back-to-front is 'ACTRESS'.
(Other definitions for actress that I've seen before include "Garland perhaps" , "Terry, say" , "one with a particular role?" , "One on stage" , "Female player" .)