cold-clock
誰が、何の目的でこんなことをしはじめたのか。死者が出た段階でもはや「ゲーム」ではありません。これ以上広がらないことを祈るのみです。
Punching Attacks in Several States Investigated for Links to 'Knockout Game'
A 16-year-old girl in London was cold-clocked by stranger in broad daylight. In Manchester, England, a man died after being punched at a bus stop. A 78-year-old woman and a 12-year-old boy were both punched in the head in separate attacks in Brooklyn.
Some law enforcement officials believe these attacks are part of a disturbing trend known as "The Knockout Game," in which perpetrators pummel innocent, unsuspecting victims. Incidents have been reported in England and in several states in the United States.
There have been at least two deaths from similar attacks this year. Surveillance video of teenagers in New Jersey shows the group running away after punching a man who then had a seizure and died.
http://abcnews.go.com/US/punching-attacks-states-investigated-links-knockout-game/story?id=21011088
cold-clockはcold-cookの異形で、「突然、（意味もなく）襲いかかる」ことを意味します。以下、Urban Dictionaryを引用しておきます。（UG）
coldclock
same thing as coldcock; to attack someone unexpectedly, usually with a blunt object and or pistol. it is often used in an attack primarily aimed at a persons head.
