Cast worth changing (5)
I believe the answer is:
throw
'cast' is the definition.
(I know that cast can be written as throw)
'worth changing' is the wordplay.
'changing' indicates anagramming the letters.
'worth' anagrammed gives 'THROW'.
(Other definitions for throw that I've seen before include "Cast, lob" , "lose on purpose" , "Confuse - cast" , "Light cloth cover for furniture" , "pitch or > floor" .)