Speculator’s target (4)
I believe the answer is:
bull
This clue is a double definition.
'speculator's' is the first definition.
(I've seen this in other clues)
'target' is the second definition.
(centre of a target)
(Other definitions for bull that I've seen before include "Cow's mate" , "Taurus in the Constellations" , "Male cow" , "Animal on target?" , "Large quadruped" .)