Cast of exceptional worth (5)
I believe the answer is:
throw
'cast' is the definition.
(I know that cast can be written as throw)
'exceptional worth' is the wordplay.
'exceptional' is an anagram indicator (an unusual or exceptional ordering of the letters).
'worth' with letters rearranged gives 'THROW'.
'of' acts as a link.
(Other definitions for throw that I've seen before include "Try to lose" , "Cast, fling" , "Toss" , "Organise party" , "Light rug" .)