Tear Up The Club was a song slated to be on Britney's 7th studio album (later named Femme Fatale). Produced by the Outsyder's (who also did Britney's lead single for Circus,
Womanizer), the song is a straight club banger!!
The Outsyder's originally revealed the demo version of the song months ago adding (paraphrase) "you'll be hearing the real thing soon" indicating it was a shoe in for the final tracklist -- in turn, Dr. Luke/Max Martin took over the project and the tracklist was probably changed, scrapping this song.
Now it features an unknown artist on the Outsyder's mixtape. You can legally download the track for free on their website
here.