The Chiefs once sold out Arrowhead Stadium every game, and owner Lamar Hunt's folksy charm endeared him to fans. But even before his death in 2006, the franchise had fallen into hard times, and it's continued under the leadership of his son, Clark Hunt, and general manager Scott Pioli.
The Chiefs are currently 1-4, and they haven't won a playoff game since 1993, a longer drought than every NFL team but Cincinnati and Detroit.
"This town just wants a winner. We just want to be relevant," said Eric Crandall, a fan from Independence, Mo., who's been attending Chiefs games for more than two decades. "The coasts refer to us as 'flyover country.' This being the town of Truman, we want the buck to stop here."
Dr. Don Forsyth, an expert in group behavior, leadership and moral judgment in the Jepson School of Leadership Studies at Richmond University, said he's not surprised by the fan backlash.
"There's a breaking point. That's the key," Forsyth said. "Fans think they're part of the team, and that's why they take wins and losses so seriously. Then when they see the administration or the leaders as the out-group, they'll engage in some pretty negative behaviors."
There are similarities in the two organizations besides won-loss records.
Both have owners who rarely speak publicly, giving them a perceived aloofness. Both franchises have been accused of being miserly, and both have made embarrassing public gaffs over the years.
In response to one angry fan, an anonymous Chiefs employee tweeted on the team's official account a few weeks ago, "Would help if you had your facts straight. Your choice to be a fan. cc get a clue." The tweet was taken down and an apology issued by the Chiefs moments later.
"You would think a team doing this poorly would try and generate some sort of goodwill with the fans," Crandall said.
The anger felt by fans was on display Sunday long before Cassel got hurt.
On one of the access roads leading into the stadium, tailgaters hung a bed sheet carrying a painted message calling the Chiefs an "embarrassment." Fans cobbled together enough money to hire an airplane to tow a banner over the stadium asking for Cassel to be benched and Pioli to be fired.
Cassel has been the source of frustration for years. He was booed lustily during a celebrity softball game this summer, and fans have been calling for his job since the start of the season.
That's part of the reason some cheered when he was hurt.
In their eyes, it was the only way the Chiefs would give backup Brady Quinn a chance.
"You never, ever, as a true fan want to see a player get injured," said Ty Rowton, also known as Chiefs super-fan X-Factor, who attended his 234th straight game at Arrowhead Stadium on Sunday.
"I didn't hear any fans cheering that Cassel was hurt," Rowton said. "When he got up and started walking from the field, the fans gave a very loud cheer, thanking him for sacrificing himself.
"There was an even bigger cheer when it was announced that Brady Quinn was going in."