Authorities say the goal is to knock a random pedestrian unconscious with a single punch.
In Lower Merion, in suburban Philadelphia, two possible "knockout" attacks have been reported this fall.
In September, an elderly man was knocked down while mowing his lawn, causing a serious injury. In late October, a 63-year-old man was punched while walking his dog.
Two 19-year-olds are charged in the second assault.
Lower Merion Lt. Frank Higgins says both attacks might be linked to the "knockout" game, since no one was robbed.
He calls it a "disturbing trend," if true.
Authorities say a victim in Jersey City, N.J., died in one such attack.