Arizona Cardinals 2015 Year in Review: A Bad Ending to a Great Season

Throughout the 2015 regular season, there arguably was no more dominant team than the Arizona Cardinals.

Sure there were those Carolina Panthers, who had the 15 wins and made it to the Super Bowl and the Denver Broncos -- eventual Super Bowl champions -- who had the league’s best defense, but Arizona was routinely the league’s most well-rounded team on a weekly basis.

Arizona spent much of the season as the top team in the league, not by record, but by our nERD metric. nERD in its simplest terms is our calculation of how good a team really is, based on expected point differential against a league average team.

From Week 3 through the end of the regular season the Cardinals were the top team in the nERD rankings. The Cardinals got there with a strong defense and the league’s best offense by Adjusted Net Expected Points (NEP) per play. NEP measures the value of each play on the field based on how an average team would be expected to score in each scenario using historical data.

The Cardinals, for how good they were for the majority of the 2015 season, had a rough and unfortunate ending.

What Went Right

In order to be the best offense in the NFL, a few things have to go right.

For much of the year, there just wasn’t much better quarterback than Carson Palmer. Palmer led the league in Passing NEP per drop back, while also having the third highest Success Rate -- the percentage of plays resulting in positive NEP -- among quarterbacks. Looking deeper into the Success Rate, Palmer had the second lowest gap for quarterbacks between his actual completion percentage (63.7 percent) and his Success Rate (52.9 percent). Basically, Palmer was one of the best at turning passes that were completed into passes that actually mattered.

Many offensive systems in today’s NFL rely on short passes that allow quick gains, but that’s not the Bruce Arians philosophy, which makes Palmer’s high Success Rate so much more impressive. The Cardinals were very much a downfield offense, looking for the home run as a focus of many plays. Palmer played his role in this offense perfectly, connecting accurately on many deep throws and leading an offense with the third most pass plays over 20 yards.

The Cardinals have a talented group of receivers between Michael Floyd, John Brown and Larry Fitzgerald, but receivers can run down the field without the ball getting placed in stride -- it happens fairly often in the NFL. Through the air, the Cardinals had a perfect balance of receivers able to get themselves open and a quarterback who could take advantage of those opportunities.

Let’s not just gloss over the production of the receivers, though.

Among the 32 receivers who saw over 100 targets, John Brown ranked 5th in Reception NEP per target and Fitzgerald ranked 22nd while being the 11th most targeted receiver in the league. Bringing the threshold down to 80 targets (five per game), Michael Floyd ranked seventh in Reception NEP per target.

On the ground, the Cardinals also likely found themselves a star in third-round pick David Johnson. Johnson spent the first part of the season as a kick returner, stuck behind Chris Johnson when the team was on offense. But an injury to the elder Johnson allowed the rookie more playing time, and with it, he became one of the biggest threats in the league with the ball in his hands. Johnson led all running backs in Rushing NEP, and among running backs with at least 100 carries, Johnson was first in Rushing NEP per attempt and Success Rate.

Arizona also did not take much of a step back after losing defensive coordinator Todd Bowles to the head coaching gig for the New York Jets. New defensive coordinator James Bettcher mostly ran an extension of the Bowles philosophy, and the Cardinals ranked seventh in Adjusted NEP per play on defense.

This team success was not highly covered in the national media, but it was not lost on many who cover the sport for this site. When we polled a group of numberFire writers at the end of the season for an awards ballot, the Cardinals were the overwhelming pick to win the Super Bowl.

What Went Wrong

Arizona, of course, didn’t win the Super Bowl -- or even appear in it -- so something clearly went wrong along the way.

One point in time that can be of reference is a Week 15 game against the Philadelphia Eagles. In that game, Carson Palmer hit his hand on Connor Barwin's helmet and dislocated his finger. Palmer was never fully his regular season self afterward. He struggled to make throws he was routinely making before the injury. That led to many throws getting intercepted, and others that had the potential to be -- something that was not the case for the majority of the season.

This played out heavily in Arizona’s two playoff games against the Packers and Panthers, Palmer’s worst two games of the season by NEP.

In that same game Week 15 against the Eagles, the Cardinals also lost Tyrann Mathieu to a torn ACL. Mathieu missed the rest of the regular season and playoffs, and a best case scenario is Mathieu returning for training camp in 2016. Mathieu was and is arguably the most important piece of the Arizona defense, and a key reason why the Cardinals ranked eighth against the pass in Adjusted NEP per play. In Arizona’s three-safety personnel, Mathieu played a hybrid role between free safety and slot corner, allowing flexibility in using Tony Jefferson and Rashad Johnson.

What’s Next?

The Cardinals are in a situation where they should be expected to continue to contend in future years, but a few key pieces, such as Palmer and Fitzgerald are reaching the last stage of their careers. While Arizona is firmly in a win-now mode, they also have younger pieces, such as David Johnson, John Brown and Patrick Peterson who form a young nucleus to keep this team competitive further into the future.

Per Spotrac, the Cardinals have around $13 million of cap space heading into the offseason. While some of that could be used to ink Mathieu to a contract extension, which has been rumored to happen, the team could also look to free agency to help with a pass rush that was one of the clear weaknesses of the roster in 2015.

Despite being a top-10 defense by Adjusted NEP, the Cardinals ranked just 19th in sack rate. The Cardinals would unlikely be players for the likes of a Jason Pierre-Paul or Olivier Vernon, but some mid-tier free agents such as Robert Ayers or Derrick Shelby could serve as help.

It’s not always easy to get back to the top of the league year after year. The Cardinals were almost there in 2014 before an injury to Palmer derailed their hopes. They came even closer in 2015 while a lesser injury to Palmer potentially had a bigger impact on how the Cardinals’ season ended.

The NFC Championship Game was a poor ending to a great season. There’s enough reason to believe -- with the leadership in place -- that it won’t be the last great season this team has.