I say it started at UFC 98.
A title unification match between the UFC Interim Heavyweight Champion Frank Mir and UFC Heavyweight Champion Brock Lesnar was originally slated to be the main event, but was postponed until UFC 100 due to a knee injury to Mir.
By way of replacement, Quinton Jackson, former UFC Light Heavyweight champion, was to fight the undefeated current champion Rashad Evans but had to undergo arthroscopic surgery to repair ligament damage in his jaw that he received in a previous training camp. Instead, Evans headlined the card against fellow undefeated contender Lyoto Machida.
The card featured the long anticipated grudge match between The Ultimate Fighter 6 coaches Matt Hughes and Matt Serra.
Due to injury, Josh Koscheck was not able to participate on this card. Brock Larson stepped in as the new opponent for Chris Wilson. Unfortunately, Chris Wilson was unable to complete the necessary medical paperwork in order to compete at UFC 98 and was replaced by Mike Pyle.
James Irvin was set to make his Middleweight debut against Drew McFedries, but was not able to fight due to a knee injury. Xavier Foupa-Pokam stepped in to fight McFedries.
Yushin Okami was set to fight Dan Miller on the main card but was injured and taken off the card, Okami suffered a torn ligament. Early reports suggested Ed Herman would replace Okami, however Chael Sonnen stepped in to take the bout.
Houston Alexander was scheduled to fight Andre Gusmao, but was forced to pull out due to a broken hand. Krzysztof Soszynski stepped in to fight Gusmao.