Spur on cowpoke's foot gashing jacket (3)
I believe the answer is:
egg
'spur' is the definition.
(I've seen this before)
'cowpoke's foot gashing jacket' is the wordplay.
'foot' suggests the final letters (in a down clue, the bottom letter).
'jacket' means to remove the middle letters (the letters worn by the word as a 'jacket' are use).
'gashing' with its centre taken out is 'gg'.
The last letter of 'cowpoke' is 'e'.
'e'+'gg'='EGG'
'on' acts as a link.
(Other definitions for egg that I've seen before include "Mine (slang)" , "Rasher to go with this" , "Food in a shell" , "It, or chicken, first?" , "Poached item?" .)