Horse is put outside the field, finally (5)
I believe the answer is:
steed
'horse' is the definition.
(steed is a kind of horse)
'is put outside the field finally' is the wordplay.
'finally' says to take the final letters.
The last letters of 'is put outside the field' are 'STEED'.
(Other definitions for steed that I've seen before include "Trusty horse" , "Warhorse" , "Powerful horse" , "Horse, mount" , "A mount (poet.)" .)