Extremely brutal Olympic association (4)
I believe the answer is:
bloc
'association' is the definition.
(I have seen 'Association of countries' mean 'bloc' so perhaps 'association' could also mean 'bloc')
'extremely brutal olympic' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'olympic' becomes 'oc' (I can't explain this - if you can you should believe this answer much more).
'brutal' with its centre taken out is 'bl'.
'bl'+'oc'='BLOC'
Can you help me to learn more?
(Other definitions for bloc that I've seen before include "Political or economic confederation" , "Alliance - coalition" , "Group acting together" , "Group with a common policy" , "People cooperating" .)