Soldier in red gear, changing (9)
I believe the answer is:
grenadier
'soldier' is the definition.
(grenadier is a kind of soldier)
'in red gear changing' is the wordplay.
'changing' is an anagram indicator.
'in'+'red'+'gear'='inredgear'
'inredgear' is an anagram of 'GRENADIER'.
(Other definitions for grenadier that I've seen before include "Soldier; fish; bird" , "Soldier - in red gear (anag)" , "Re-reading for the deep-sea fish" , "African flier" , "guard" .)