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As the NFL offseason officially begins after Super Bowl 50 ends, NFL general managers must evaluate their core rosters. Key free agents and breakout players must be identified and prioritized. One player who greatly raised his value in 2015 was Washington Redskins quarterback Kirk Cousins.

After winning the NFC East and playing on Wild Card Weekend against the Green Bay Packers, the Redskins may feel as if they have their franchise quarterback. Cousins may prove to be an above-average quarterback in time, but he fell short of that in 2015. Based on the film he produced, the Redskins must avoid rewarding Cousins with a long-term investment.

The raw statistics Cousins produced were impressive at face value. Take a look at his numbers and where they ranked compared to his peers.

Kirk Cousins' Regular-Season Statistical Ranking Kirk Cousins' Total NFL Ranking Completions 379 7th Attempts 543 12th Completion Percentage 69.8% 1st Yards 4,166 10th Touchdowns 29 13th Interceptions 11 15th Yards Per Completion 11.0 28th Yards Per Game 260.4 14th Pro-Football-Reference.com

What the Redskins must ask themselves is what the cause of Cousins’ production was. While it’s not inconceivable that Cousins suddenly transformed from a high-end backup to a top-10 quarterback, his transformation raises red flags. To help figure out whether Cousins’ success is sustainable, I went back and watched every snap of his in 2015.

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To measure Cousins’ effectiveness beyond the stat book, I also charted his passes to get a large snapshot of the offense as a whole and to isolate the quarterback’s performance. By tallying his directional accuracy, we can compare Cousins to his peers across the NFL. I am defining accuracy as a pass that is reasonably catchable by his target, not one that is tipped or requires an extravagant effort by the receiver.

Kirk Cousins' full 2015 accuracy chart. Accurate pass = catchable pass. #Redskins pic.twitter.com/Xm1Wu0FMdi — Ian Wharton (@NFLFilmStudy) January 29, 2016

Above, we can see a breakdown of Cousins’ accuracy from 2015, including the playoffs. After taking out throwaways and shovel passes, Cousins delivered a solid accuracy score of 72 percent. This is good, but his lack of downfield accuracy and penchant for dumping the ball off are concerning.

A whopping 68 percent of Cousins’ passes were either behind the line of scrimmage or less than 10 yards. Comparatively, the NFL average for all 32 teams is 60 percent, according to Pro Football Focus. Even statistically, the Redskins’ inability to go downfield was evident, as Cousins had the seventh-most passing attempts but the 28th-highest yards per completion.

Some notable offenses and quarterbacks around the NFL run similar short-passing attacks—most notably, the New England Patriots and the New Orleans Saints. With their aging quarterbacks, they’ve found it is more efficient to throw it short and intermediately. But they also have Tom Brady and Drew Brees, respectively.

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The difference for the Redskins is how limited Cousins is as a passer. Despite his shining completion percentage of 69.8 percent, Cousins is not overly accurate unless he’s throwing the ball on short routes. His arm strength isn’t the only issue, but his footwork and poise in the pocket often cause him to miss easy throws.

In the rare occurrence that Cousins actually tried to thread the needle on downfield passes, his arm simply lacked the zip to get the ball where it needed to be. His lower body often shows a wide base, and he doesn’t have the pure arm strength or core strength to drive the ball. His passes die at the tail end and become easy targets for defenders.

Kirk Cousins' accuracy chart against teams with winning records in 2015 pic.twitter.com/jh6n5zWBc7 — Ian Wharton (@NFLFilmStudy) January 29, 2016

The dangerous, misguided throws plagued Cousins throughout the season. They were especially apparent against winning teams, and Cousins’ performance noticeably dipped against top competition. See above for Cousins’ accuracy chart against winning teams in 2015.

While the accuracy charts are subjective, the statistics also reflect a considerable drop in production. Washington played the 22nd-ranked strength of schedule, and just six teams had eight or more wins. Cousins and the Redskins couldn’t control that, but it is concerning that Cousins struggled so much in games against these opponents.

Kirk Cousins' Averages Against Winning Teams in 2015 Completions Attempts Completion Percentage Yards Touchdowns Interceptions Passer Rating 19.8 31.8 62.2% 194.6 .83 1 62.8 Pro-Football-Reference.com

Proponents of Cousins, as well as his agent, will point to the statistical run he went on from Week 7 until the playoffs. That 10-game stretch featured 23 passing touchdowns and three interceptions. Although impressive, this run was similar to what Nick Foles accomplished with the Philadelphia Eagles in 2013.

Infamously, Foles benefited from an excellent offensive scheme and good fortune to throw 27 touchdowns and two interceptions in 10 games started in 2013. He regressed badly the next season, but his film was the same. His erratic tendencies were never fixed. Defenses changed the way they played him, and he couldn’t readjust.

Now, I’m not willing to say Cousins is in the same class as Foles. Foles was one of the worst quarterbacks in the NFL the last two seasons. Cousins is better than Foles, but it is important to keep his 2015 in perspective.

In Cousins’ "hot streak," he did show improvement in his accuracy and decision-making. The change was marginal, though. His accuracy improved just 4 percent in my charts despite the impressive touchdown-to-interception ratio in the second half of the season.

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Some may point to the raw stats to say Cousins got better with every start, but he wasn’t doing anything more special down the stretch. The Saints game is a great example. Cousins completed 20 of 25 passes for 324 yards and four touchdowns, but just five passes traveled past 11 yards in the air.

The biggest reasons for the Redskins’ offensive improvement were a great offensive design, tight end Jordan Reed’s ascension into elite status, a terrific pass-blocking offensive line, the quality play of secondary receivers and the threat of DeSean Jackson. Defenses were gashed, as they couldn’t get to Cousins with regularity or cover their playmakers long enough.

Reed’s incredible play was the biggest revelation of the season. He dominated opposing defenses to the tune of 87 receptions, 952 yards and 11 touchdowns. He hit 100 yards in three of the last five regular-season games and had six touchdowns. Reed was the catalyst to the Redskins’ offensive explosion.

Looking at their per-play production, the Redskins had a poor running game. With an average of just 3.7 yards per carry, this is an area they can improved. But the threat of the run action helped the passing game. Cousins’ passer rating was a full 25 points better when using play-action fakes, according to Pro Football Focus.

When breaking down the Redskins offense, it is clear how much opponents respected their deep playmaker core and excellent scheme. Head coach Jay Gruden and offensive coordinator Sean McVay did a fantastic job creating underneath space for Cousins to work with. Cousins does not do well working off his first read, so it was imperative the running backs and receivers got open quickly.

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Even prior to Cousins’ breakout stretch, Gruden earned the respect of film junkie and MMQB analyst Andy Benoit. Benoit lauded Gruden’s offensive design to 106.7 The Fan’s Chad Dukes (h/t Chris Lingebach of CBSDC.com) on October 14, 2015: “Gruden, he’s a top-10 NFL head coach right now, just going by game-planning.”

That’s high praise, but his game-planning stood out to me as well. Gruden and McVay did an excellent job utilizing their best playmakers and playing to Cousins’ strengths. While Cousins executed nicely, he was simply playing within a defined role that asked him to do little.

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Whenever Cousins was required to create on his own or carry a larger burden, he struggled. The recklessness and variance Cousins shows when he is pressured or outmatched is alarming—especially once we look at the potential long-term deal he could receive this offseason.

On 106.7 The Fan's Grant & Danny (h/t Bryan Frantz of CBSDC.com), CBS Sports salary-cap expert Joel Corry opined in December that Cousins could be looking for a deal averaging at least $17 million a season:

If he plays lights out [to end the season], the agent’s going to be thinking "you need to pay him as a top-tier quarterback, even though it’s only been one year." If not, you’re talking the high end of the second tier, and you’ve got to think that Ryan Tannehill would be the floor. That’s $77 [million] over four [years]. But you want it structured better than his, because Tannehill has $21.5 million fully guaranteed at signing, $45 million [guaranteed] overall; you’re going to want more fully guaranteed than that at signing. But that would be what the agent would call the floor.

We know that Cousins did end up playing well after those comments, which Corry made on December 23, 2015. But that salary would put Cousins in a category in which he simply doesn’t belong. See below for the other quarterbacks making between $16 million and $20 million in total cash for 2016.

The issue with the timing of Cousins’ breakout isn’t that he’s a bad player; rather, he’s an average quarterback who executes with an excellent supporting cast. But giving a massive deal to Cousins this offseason doesn’t make sense for a limited player at quarterback. It is difficult and expensive to continue supplying high-end playmakers on one side of the ball, especially when paying a quarterback a major salary.

If the Redskins feel pressured to do it because they won’t find an obvious upgrade this offseason, then they must configure the contract carefully. Recent major deals like Colin Kaepernick's and Andy Dalton’s have easy and relatively inexpensive outs just two years into the contracts.

There is a better option, though.

The Redskins should use their franchise tag on Cousins for 2016. While this option is the most expensive for the short term, it allows the team to be flexible at the position moving forward. If a top quarterback prospect falls to the Redskins in the draft, they can invest in one and start Cousins in 2016 to see if he can continue improving.

Whether Cousins gets better or regresses, the team can move either him or the other quarterback for assets much easier without committing a long-term deal to Cousins. Even if Cousins shows great improvement next year on intermediate and deeper throws and shows more ability making progressions, his cost is unlikely to greatly change in 2017.

He’s already looking at a top-10 quarterback contract, so paying him after he has another season to show his talent level is a solid risk by the team. What Cousins must prove in 2016 is that he has the talent to be an above-average quarterback and won’t be stuck as a middling quarterback with a clear ceiling.

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Based on his 2015 play, he’s a serviceable quarterback. There were several instances that Cousins hit big-money throws and absolutely justified Gruden’s decision to start him at the beginning of the season. There’s no doubt he has earned the right to enter 2016 as the starter.

But the concern that Cousins will stagnate is realistic and worrisome. Serviceable quarterbacks rarely win big games in the NFL. For the Redskins to make the jump, they need flexibility with Cousins until he proves he can be the franchise quarterback.

All stats used are from Sports-Reference.com.

Ian Wharton is an NFL Featured Columnist for Bleacher Report.

Follow @NFLFilmStudy