Go on, chuck final! (4-5)
I believe the answer is:
last-ditch
'final' is the definition.
(I've seen this before)
'go on chuck' is the wordplay.
'go on' becomes 'last' (I've seen this in another clue).
'chuck' becomes 'ditch' (both can mean to abandon or throw away).
'last'+'ditch'='LAST-DITCH'
(Other definitions for last-ditch that I've seen before include "Denoting final attempt (to do something)" , "Stitch lad up in final defence" , "Of an attempt or stand, final and desperate" , "Eleventh-hour" , "Final recourse" .)