The One in Ten Rule

One of my friends, a veteran street fighter used what he
called the 'one in ten rule'. His theory (and he made it work
many times) was that if you can find the leader of a gang of
ten men, and control him, then you automatically controlled
the other nine.
He was a pub landlord and whenever he took over a new
pub he'd find out over the first few weeks who the ring
leader was, who played up, who was chancing their arm as it
were. Once he knew he would choose the right moment and
separate the one from the ten and take him into the cellars
saying that he had a proposition. Once in the cellars he
would lock the door and offer the guy a 'square go', a match
fight. Due to my friend's fearsome reputation as a fighter,
they would invariably bottle it at this point and he'd warn
then never to cross him again.