Examining DeSean Jackson's Impact on the Rise and Fall of Chip Kelly

Chip Kelly talk is dominating print, TV and talk-radio, with recent articles on whether the Eagles’ owners will fire Chip Kelly, and if Kelly’s coaching is the problem or his personnel moves.

Kelly unceremoniously dumped wide receiver DeSean Jackson last offseason, supposedly for “football reasons,” although Jackson was coming off of a strong season with 82 receptions for 1,332 yards and 9 touchdowns -- all career highs.

Meanwhile, Jackson has been back to doing his thing recently with Washington: streaking down the field wide open for long touchdowns. Kirk Cousins certainty should appreciate Jackson’s return -- the speedy wideout accounted for both of Cousins’ touchdowns the last two weeks.

You’ll notice something interesting if you look at a longer timeframe of how Cousins has performed with and without Jackson in the lineup. Cousins is a highly efficient quarterback with Jackson, averaging 7.6  adjusted yards per attempt (a metric that combines yards per attempt, touchdowns, and interceptions), or roughly the same as Peyton Manning during his career.

Without Jackson, Cousins has been as uninspiring as they get with an AY/A of 5.5, in the ballpark of Rex Grossman.

The stunning difference in Cousins’ performance with and without Jackson led me to take a deeper look at the effect Jackson has had on all of the quarterbacks he’s played with throughout his career. In the end, I came to a striking conclusion: DeSean Jackson is one of the most valuable receivers in the NFL.

In football, it is particularly difficult to analyze player performance due to the interdependence of actors. How much of a running back’s stats are due to his talent? His offensive line? The fact that a strong passing game means that he’s playing often with a lead? You can’t simply say that stats-equal-performance like in baseball and its isolated pitcher-batter interactions.

One way to improve the assessment of receiver talent is to adjust statistics for efficiency, instead of focusing on raw numbers. The simplest and most effective way to do that is to look how efficient a quarterback is throwing the ball to a particular receiver.

Narrowing the analysis on the efficiency of only passes to an individual receiver helps you assess how efficient a team is when throwing to that receiver, but it doesn’t account for the effect that receiver is having on offense when he isn’t targeted.

When a defensive coordinator designs a scheme to limit a particular receiver -- either with double coverage or shadowing with his best cornerback -- more resources are being dedicated to that receiver, leaving less to defend the rest of the field.

In a scenario like we saw last week with  Richard Sherman shadowing Antonio Brown, the contributions of the Steelers’ leading receiver will be understated by his receiving numbers. Brown’s presence was making it easier for Ben Roethlisberger by allowing Markus Wheaton to put up career numbers while facing lesser coverage.

To assess DeSean Jackson’s value, I’m going to use one of my favorite metrics that solves the issue of how to assess the impact of a wide receiver even when he's not being thrown the ball.

Neil Paine developed WOWY (with-or-without-you) in a post for Football Perspective, then worked with FiveThirtyEight colleague Benjamin Morris to refine and apply WOWY to the case for Randy Moss being the greatest receiver of all time. The key to the WOWY concept is that you’re controlling for passer quality by focusing on the difference in performance for individual quarterbacks when they are playing with or without a particular receiver. This allows you to assess not only the benefit when throwing to a particular receiver, but to account for that receiver’s effect on the entire passing game, which is reflected in the quarterback’s overall stats.

When we look at the difference in quarterback passing efficiency playing with and without Jackson over the years, the results are stark.

Nick Foles, Cousins, and Michael Vick, in particular, were significantly better with Jackson, playing like all-time greats as opposed to mediocre passers the rest of their careers. 

The only quarterback that Jackson’s presence didn’t benefit was Robert Griffin III, and there’s a good reason that’s the case. Griffin’s was a revelation his rookie season (8.6 AY/A), but injuries and a historic regression in efficiency rendered the former-star a diminished talent ever since. Jackson wasn’t in Washington during Griffin’s rookie year, so it’s no surprise that Griffin’s with-Jackson numbers are lower.

But if you only look at post-rookie Griffin, his AY/A with Jackson exceeds without by 7.0 to 6.6. Looking just at AY/A, five of six of Jackson’s quarterbacks (minimum 8 games and 200 attempts in “with” games) are more efficient with Jackson than without. On average, Jackson has improved his quarterback's performance by +1.2 AY/A. A difference in AY/A of +1.2 doesn’t sound like much, but it’s roughly the equal to the gap in career averages between Drew Brees and Charlie Batch.

Knowing what we now know about how impactful Jackson is as a receiver, could the downfall of Kelly’s high-powered offense be more about the loss of Jackson than coaching issues or other personnel decisions?

The offense efficiency metrics certainly back that up. Eagles’ quarterbacks under Kelly averaged 9.0 AY/A with Jackson in the lineup, and only 6.5 without.

In 2013, with Jackson, the Eagles had the fifth-best offense by our Adjusted Net Expected Points metric but were 15th in 2014 and are 28th this year.

I’m sure there are other contributing factors to the Eagles’ offense collapse, but losing a wide receiver who consistently turns mediocre quarterback play into Pro Bowl worthy numbers is going to have a hugely negative effect.

The rise and fall of Chip Kelly can be framed as a story of genius failed or a coach who “lost” the confidence of his team. But, the simpler and possibly more accurate explanation is that coaching can only take a team so far, and filling the void left by a game-changing talent like DeSean Jackson isn’t as simple as replacing a cog in a machine.