Pal mob's jostling showing sangfroid (6)
I believe the answer is:
aplomb
'sangfroid' is the definition.
(I've seen this before)
'pal mob's jostling' is the wordplay.
'jostling' indicates an anagram (letters move or jostle around).
'pal'+'mob'='palmob'
'palmob' is an anagram of 'APLOMB'.
'showing' acts as a link.
(Other definitions for aplomb that I've seen before include "Nonchalant confidence" , "Pompous dignity or poise" , "Cool self-assurance" , "Self-satisfied assurance" , "Self-satisfied poise" .)