Fighter in his early years needing extra weapon (8)
I believe the answer is:
claymore
'weapon' is the definition.
(I've seen this before)
'fighter in his early years needing extra' is the wordplay.
'fighter in his early years' becomes 'clay' (Muhammad Ali was born Cassius Clay).
'needing' is a charade indicator (letters next to each other).
'extra' becomes 'more' (I've seen this before).
'clay'+'more'='CLAYMORE'
(Other definitions for claymore that I've seen before include "Scottish sword wielded by my oracle" , "Highland weapon" , "pipe" , "Scottish highlander's sword" , "Two-edged broadsword" .)