No. 1: Mark Sanchez's shoulder injury
It happened in the preseason, but it may have changed the complexion of the entire season. In the fourth quarter of the third preseason game, against the New York Giants, Rex Ryan decided to insert Sanchez. It was a questionable call on face value alone, but two other factors made it a downright terrible decision: At that point, Sanchez was the presumptive, opening-day starter, as Geno Smith bombed that night in his audition for the job. Secondly, Ryan put Sanchez in harm's way by playing him behind the second-team offensive line, not the starters.
It was an unmitigated disaster. Matt Simms was warming up, seemingly preparing to replace Smith, but the call went to Sanchez, who was caught off guard and warmed up quickly. He was under siege from the first play. On his third series, rolling to his left on a scramble, he was blasted at full speed by defensive tackle Marvin Austin. He hit Sanchez so hard that it tore the labrum in his throwing shoulder -- although it took a few weeks before the Jets finally came clean, admitting he needed surgery. It probably will end up being his last play as a Jet.
Things got weird after the game, when Ryan, in a combative news conference, insisted his reasoning for playing Sanchez was because he wanted to win the game and the Snoopy MetLife Trophy. Ryan was so annoyed by reporters questioning his decision that he actually turned sideways at one point.
The Jets had no choice but to start the season with Smith, who wound up starting every game. Sanchez's injury created so many what-if questions: What if Sanchez had started the season? Would he have thrived in Marty Mornhinweg's system? If not, how long before he was replaced by Smith? There probably would've been a full-blown quarterback controversy at some point. We'll never know.