First Heard at a Sporting KC game: Opening night at LIVESTRONG park against Chicago, June 9th, 2011. Not sure if this dates back to Wizards days.
Based off of: Unknown. Apparently this was originated at the Naval Academy and dates back to 2003. The earliest recording I can find of the Naval Academy chanting "IBTWWW" is 2009. But they did have shirts printed up in 2003 with "I Believe That We Will Win." Recordings of this showed up from college basketball teams like Utah St. and SDSU around 2009/10. It is also known to be head at US Men's National Team games.
History since 2011: Sporting KC used #IBelieveThatWeWillWin as part of the playoff marketing campaign with full paged ads, encouraging of the hashtag on Twitter and changes to their main home page. In 2012, IBTWWW was used as part of the ad campaign for the newly branded NBC Sports Network (formerly Versus)
Associated movement: Usually jumping in place (pogo-ing) once you get to the final line at LIVESTRONG. Others have pumped their fist (or two in the air with each crowd chant)
Lyrics: (Call and Response)
Leader: I believe
Crowd: I believe
Leader: I believe that
Crowd: I believe that
Leader: I believe that we
Crowd: I believe that we
Leader: I believe that we will win!
Crowd: I believe that we will win!
(until crowd starts to quiet)
(Often resarted after fade out maybe 2 or 3times max)
When you'll hear it: Maybe late in the first half if still scoreless, usually after a goal that gives us a lead, rarely after a goal that gets us equal. Possibly late in the game
Listen to it recorded from LIVESTRONG Sporting Park:
"I Believe That We Will Win" Sporting Kansas City (downloadable) by AdAstraSKC
Sporting Kansas City 2011 Playoff Ad
Other MLS Clubs using it: New York Red Bulls (2010), Columbus Crew (2011)
Find it on Twitter with Hashtag #IBTWWW If you have more information on this chant, please comment below and will get the post updated.