Little ball from gym upset famous archer (6)
I believe the answer is:
pellet
'little ball' is the definition.
(I've seen this in another clue)
'gym upset famous archer' is the wordplay.
'gym' becomes 'pe' (short for Physical Education).
'upset' shows that the letters should be reversed in order.
'famous archer' becomes 'Tell' (William Tell).
'tell' in reverse letter order is 'llet'.
'pe'+'llet'='PELLET'
'from' is the link.
(Other definitions for pellet that I've seen before include "Small bullet" , "Piece of shot for gun" , "Light bullet" , "Shot -- slug" , "Small pill" .)