Considered ascendant when he had a breakout season with the New England Patriots in 2008, Cassel was supposed to step in and become the Chiefs' franchise quarterback.
And despite some big-time struggles in Cassel's first season with the team in 2009, he looked on the verge of doing just that in 2010. The 30-year-old quarterback threw for 3,116 yards and 27 touchdowns against just seven interceptions en route to leading Kansas City to the playoffs and making his first Pro Bowl.
Unfortunately for the Chiefs, what looked like an upward trajectory was only an anomaly, and the facade of Cassel as an NFL starting quarterback has been crashing down ever since.
Last season saw Cassel return to his ineffective self and play in just nine games due to a hand injury. Though his standard statistics (1,713 YDS, 10 TDs, 9 INTs, 76.6 QB Rating) in 2011 were not horrible, his true deficiencies can be spelled out through advanced metrics.
Using Football Outsiders' DVOA (Defense-adjusted Value Over Average) metric, Cassel ranked 39th out of 47 qualifying players last season, providing the Chiefs with 20.2 percent less production than a replacement-level quarterback.
While one could chalk that up to Jamaal Charles' injury hampering the Kansas City offense, that ranking almost perfectly mirrors his aforementioned struggles in 2009.
What's more, these failures have only continued thus far this season. Only this time around, it's not even necessary to use the advanced metrics.
Cassel threw three interceptions against the San Diego Chargers in the first half of last week's game, ostensibly stripping the Chiefs of a chance to win while putting up insignificant numbers in garbage time.
Well, that is apparent to seemingly everyone except Chiefs head coach Romeo Crennel.
Here is Crennel talking about the quarterback situation, via CBS Sports:
Matt is the quarterback. What he has been able to show is that he can make plays. Even after he had those turnovers, he came back and drove the team down the field. We think he is capable, and we just have to get him to be more consistent. (Sunday) the whole team needed to be more consistent. You see flashes of it. You just don't see it consistently.
Let's make one thing abundantly clear: Quinn is certainly not a long-term fix. In his only season with significant work in 2009 with the Cleveland Browns, Quinn completed just 53.1 percent of his throws and was the 30th-ranked quarterback according to Football Outsiders' metrics.
However, it's easy to argue that Quinn never got a fair shake in the NFL. His only season as a starter was on an offense boasting a rookie Mohamed Massaquoi as the No. 1 receiver, and a washed-up Jamal Lewis and Jerome Harrison as the running backs. There are a select few players in league history that could perform admirably with that motley crew of skill position talent.
Even over two full seasons removed from throwing an NFL pass, you have to wonder what Quinn could do with an offense boasting Jamaal Charles and Dwayne Bowe.
There is also something to be said for having a different voice in the huddle. With the way Cassel has played this season, there cannot be any confidence left from the coaching staff or fellow offensive starters that he's the man for the job.
With the season in peril, there is literally nothing left to lose by benching Cassel and starting Quinn. If the former Notre Dame star is an unmitigated disaster, it's not as if Cassel will be banished from the locker room and unable to reclaim his spot.
However, by avoiding making a change, Crennel is seemingly allowing fear of the unknown to dictate his decisions.
Considering how paltry Cassel's play has been this season, it's time for Kansas City to wade into those unknown waters.