April 16, 2011: Hoang Nguyen, 72, is attacked in a St. Louis alley and killed by 20-year-old Elex Murphy.
Oct. 10, 2012: James Addlespurger is attacked by a 15-year-old boy walking down the street in Pittsburgh.
Feb. 26, 2013: Marvell Weaver is shot twice by the .40 caliber pistol of a man he was attempting to knock out with a stun gun in Lansing, Mich.
May 23, 2013: Michael Daniels is beaten to death by a group of teenagers outside of Los Amigos Grocery in Syracuse, N.Y.
Aug. 22, 2013: WWII veteran Delbert Belton is beaten to death in the parking lot of a local Eagles Lodge in Spokane, Wash.
Sept. 10, 2013: In Jersey City, two 13-year-olds and a 14-year-old are charged with the beating death of Ralph Eric Santiago.
Nov. 12, 2013: A 19-year-old Jewish man is reportedly "sucker punched" in Brooklyn.
Nov. 14, 2013: A woman said she was swarmed by a group of teenagers on bikes and attacked on in the Columbia Heights area of Washington, D.C.
Nov. 16, 2013: A 78-year-old Midwood, Brooklyn, woman is punched in the face.
Nov. 23, 2013: Amrit Marajh allegedly attacked Shmuel Perl in Brooklyn. He is charged with third-degree assault, assault as a hate crime and aggravated harassment as a hate crime.
There is little to no evidence that teenagers are publicly sharing "knockout" videos on social media, and law enforcement officials have been reluctant to label the various attacks.
Ryan Broderick is a reporter for BuzzFeed News and is based in London.
Contact Ryan Broderick at firstname.lastname@example.org.
Got a confidential tip? Submit it here.