Snowballs, in a snowball fight (4)
I believe the answer is:
ammo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">snowballs in a snowball fight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ammo that I've seen before include "Bullet" , "Bullets, shells (colloq.)" , "Bullets, shells, etc. (abbr.)" , "Bullets, etc. (colloq.)" , "Contents of magazine" .)