Veteran soldier who rears bats (8)
I believe the answer is:
warhorse
'veteran soldier' is the definition.
(I've seen this before)
'who rears bats' is the wordplay.
'bats' is an anagram indicator (slang for mad).
'who'+'rears'='whorears'
'whorears' with letters rearranged gives 'WARHORSE'.
(Other definitions for warhorse that I've seen before include "something too often played" , "Belligerent" , "Old soldier" , "steed?" , "Veteran soldier" .)