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' is an anagram indicator.
'by' means one lot of letters go next to another.
'unruly' indicates an anagram.
'pal' with letters rearranged gives 'apl'.
'mob' is an anagram of 'omb'.
'apl'+'omb'='APLOMB'
'of' is the 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" .)