Killing/beheading scoundrel in concert (6)
I believe the answer is:
pogrom
'killingbeheading' is the definition.
I can't tell whether this defines the answer.
'scoundrel in concert' is the wordplay.
'scoundrel' becomes 'og' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'concert' becomes 'prom' (abbreviation for promenade concert).
'og' put into 'prom' is 'POGROM'.
Can you help me to learn more?
(Other definitions for pogrom that I've seen before include "Organised persecution of an ethnic group" , "Racial massacre" , "Mass slaughter" , "Organised massacre of Jews" , "An organised massacre of a people" .)