Coolness of pal injured by unruly mob (6)
I believe the answer is:
aplomb
'coolness' is the definition.
(I know that coolness can be written as aplomb)
'pal injured by unruly mob' is the wordplay.
'injured' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'unruly' indicates anagramming the letters.
'pal' anagrammed gives 'apl'.
'mob' is an anagram of 'omb'.
'apl'+'omb'='APLOMB'
'of' acts as a link.
(Other definitions for aplomb that I've seen before include "Cool self-confidence" , "Self-satisfied dignity and confidence" , "Cool self-assurance" , "Dignified self-confidence" , "Great coolness and composure under strain" .)