Worth altering the cast (5)
I believe the answer is:
throw
'the cast' is the definition.
(I've seen this in another clue)
'worth altering' is the wordplay.
'altering' indicates anagramming the letters.
'worth' is an anagram of 'THROW'.
(Other definitions for throw that I've seen before include "Discard" , "Light rug" , "Make a pot" , "Cast; give (party)" , "Hurl; perplex" .)