Communist not best pleased in humanitarian group (3,5)
I believe the answer is:
red cross
'group' is the definition.
(Red Cross is an example)
'communist not best pleased in humanitarian' is the wordplay.
'communist' becomes 'red' (red is a kind of communist).
'not best pleased in humanitarian' becomes 'cross' (I am not sure about this - if you are sure you should believe this answer much more).
'red'+'cross'='RED-CROSS'
Can you help me to learn more?
(Other definitions for red cross that I've seen before include "International team" , "International organisation for treatment of wounded in war" , "flag" , "Intl. relief agency" , "International movement" .)