Pierce, producing blood (4)
I believe the answer is:
gore
This clue is a double definition.
'pierce' is the first definition.
(goring is a kind of piercing)
'blood' is the second definition.
('gore' can be a synonym of 'blood')
'producing' acts as a link.
(Other definitions for gore that I've seen before include "Spilt blood" , "Blood; stab with tusk" , "Pierce with horn - blood" , "stuff from part of Kensington" , "Bloodshed" .)