I had no idea, so :
One night in October 1986, [Dan] Rather was walking down a Manhattan street when he was punched from behind and thrown to the ground. His assailant kicked and beat him while repeating, “Kenneth, what is the frequency?”
No one could explain the event, and the rumors flew fast and wide. Some speculated the assailant was a KGB agent, while others claimed the attack was the work of a jealous husband. Rather himself couldn’t shed any light on the subject…
Apparently the strange event moved R.E.M. singer Michael Stipe, who said of the incident:
It remains the premier unsolved American surrealist act of the 20th century. It’s a misunderstanding that was scarily random, media hyped and just plain bizarre.
The attack inspired the 1994 R.E.M. hit “What’s the Frequency, Kenneth.”