Rampaging mobs hesitated and lost an opportunity (6,3,4)
I believe the answer is:
missed the boat
'lost an opportunity' is the definition.
(I've seen this before)
'rampaging mobs hesitated' is the wordplay.
'rampaging' is an anagram indicator (I've seen this in other clues).
'mobshesitated' is an anagram of 'MISSED THE BOAT'.
'and' acts as a link.
(Another definition for missed the boat that I've seen is " Lost an opportunity".)