Amateur joins theatre for show again (6)
I believe the answer is:
replay
'show again' is the definition.
(to show a TV show again)
'amateur joins theatre' is the wordplay.
'amateur' becomes 'lay' (similar in meaning).
'joins' is a charade indicator (letters next to each other).
'theatre' becomes 'rep' (repertory theatre).
'lay' after 'rep' is 'REPLAY'.
'for' acts as a link.
(Other definitions for replay that I've seen before include "Second showing?" , "Hold match again" , "A cup tie; clip shown over and over" , "kind of race" , "Repeat recording of part of game" .)