Singer forced to quit (6)
I believe the answer is:
resign
'to quit' is the definition.
(I know that resign is a more specific form of leave office)
'singer forced' is the wordplay.
'forced' is an anagram indicator.
'singer' anagrammed gives 'RESIGN'.
(Other definitions for resign that I've seen before include "Give up office" , "Step down" , "Give up one's job" , "Stand down" , "surrender" .)