Leading man I don't cast (8)
I believe the answer is:
dominant
'leading' is the definition.
(I've seen this before)
'man i don't cast' is the wordplay.
'cast' is an anagram indicator (letters are dispersed or cast around).
'man'+'i'+'dont'='manidont'
'manidont' anagrammed gives 'DOMINANT'.
(Other definitions for dominant that I've seen before include "Strongest - ruling" , "Most influential; fifth of scale" , "Foremost, main" , "alpha male?" , "note?" .)