Rage about extremely volatile person seeking to retaliate (7)
I believe the answer is:
avenger
'person seeking to retaliate' is the definition.
'rage about extremely volatile' is the wordplay.
'rage' becomes 'anger' (I've seen this before**).
'about' is an insertion indicator.
'extremely' means to remove the middle letters.
'volatile' with its middle removed is 've'.
'anger' placed around 've' is 'AVENGER'.
(Other definitions for avenger that I've seen before include "One getting his own back" , "One exacts retribution" , "Someone wanting to get even" , "One taking retribution" , "Hillman" .)