Small fruits become weapons (6)
I believe the answer is:
spears
'weapons' is the definition.
(spear is a kind of weapon)
'small fruits' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'fruits' becomes 'pears' (pear is a kind of fruit).
's'+'pears'='SPEARS'
'become' acts as a link.
(Other definitions for spears that I've seen before include "Lances" , "Bits of green veg" , "Long weapons with a sharp points" , "Stems of asparagus as weapons" , "Long pointed weapons" .)