The brief line for cast (5)
I believe the answer is:
throw
'for cast' is the definition.
(synonyms)
'the brief line' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'line' becomes 'row' (a row or line of things).
'the' with its final letter taken away is 'th'.
'th'+'row'='THROW'
(Other definitions for throw that I've seen before include "Organise party" , "Confuse - cast" , "Try not to win" , "pitch or > floor" , "Cast; give (party)" .)