PART 1: Conception (Wikipedia)
It has become a popular culture cliché for the audience of almost any concert to shout "Free Bird" as a request to hear the song, regardless of the performer or style of music...This can be traced back to Skynyrd's first live album, 1976's One More From The Road. Skynyrd did not play the song during the main portion of the concert, or even in the encore performance. Instead they saved it for their second encore. After leaving the stage following the first encore of the concert, the crowd was riled by the apparent omission of Skynyrd's signature song. The crowd then began chanting "Free Bird, Free Bird ...". No one left the auditorium. The band then returned to the stage... asked the crowd, "What song is it that you wanna hear?"...[and then] responded with a 14-minute version of the song....
PART 2: Birth and Maturity ( The Wall Street Journal)
Apparently though the official credit goes to a Chicago Radio DJ named Kevin Matthews. No less than The Wall Street Journal has a great article on the phenomenon including this little bit of Kevin's Part in the requests history.
Kevin Matthews is a Chicago radio personality who has exhorted his fans -- the KevHeads -- to yell "Freebird" for years, and claims to have originated the tradition in the late 1980s, when he says he hit upon it as a way to torment Florence Henderson of "Brady Bunch" fame, who was giving a concert. He figured somebody should yell something at her "to break up the monotony." The longtime Skynyrd fan settled on "Freebird," saying the epic song "just popped into my head."
Mr. Matthews says the call was heeded, inspiring him to go down the listings of coming area shows, looking for entertainers who deserved a "Freebird" and encouraging the KevHeads to make it happen.
Currently listening: Free Bird - Lynyrd Skynyrd