Unexpectedly, Case Keenum has become critical to the function of the Vikings offense, and has played a quarter of the team’s 16-game season as the primary quarterback. There seems to be a good chance that Keenum will continue to play a big role in fulfilling the Vikings’ playoff dreams, especially with Sam Bradford’s re-injury.

The former Houston quarterback — both for the Texans and the Cougars — was benched for Jared Goff last year, who then turned in the worst performance in the NFL among starting quarterbacks. The Vikings signed him in the offseason with the assumption that he would be an above-average backup with veteran experience in case anything happened to their injury-prone starting quarterback.

As it so happened, the injury-prone passer sustained an injury, and Keenum was called into action. Short on prep, he underperformed against the Pittsburgh Steelers but impressed the next week against the Tampa Bay Buccaneers. With two more performances on the books, the backup quarterback has done more than anyone could have reasonably expected and now has helped the Vikings to a 2-2 record in games where he was the primary quarterback.

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His statistical profile is fairly remarkable. One can look at a number of different quarterback metrics to check in on Keenum’s progress thus far.

Statistic ANYA QBR Passer Rating Yards Per Attempt PFF Grade PFF “Rating” Rank 6 5 10 13 9 10

ANYA is adjusted net yards per attempt, which is meant to replace passer rating with weights that more closely correlate to winning. ESPN QBR’s rating tracks more closely with winning than nearly any other measurement. It’s built off of a proprietary formula that works in part by assigning an “expected points” value to each spot on the field, adjusted for down and distance.

Everything else is fairly well-known to football fans, though it’s worth noting that “PFF Grade” and “PFF Rating” are different — Pro Football Focus assigns a grade to each play for each player in a game, handing out demerits for passes that should have been intercepted and giving credit to accurate passes that were otherwise dropped.

The “rating” is just Pro Football Focus modifying the traditional passer rating to account for spikes, throwaways and receiver drops.

Regardless of the specifics of each metric, it’s pretty clear that Keenum has performed as, generally, a top-10 quarterback.

While no one would expect that to continue over the course of the season, it does speak to how ably Keenum has stepped into his role. He is performing above the level anyone could expect from a backup quarterback.

His aggregate statistical profile is interesting, but not revealing — it tells us how well he’s been playing, but not how he’s playing. For that, we can dive into some splits.

Keenum’s passing profile is largely average — he has a league-average amount of time in the pocket, a league-average shotgun usage rate, and uses play-action at a league-average rate. There are a few elements to his profile that is distinctive, however:

Statistic Time to Sack Time to Run Time to Throw Time in Pocket Rank 32 22 15 11

Statistic Pressure Rate Play Action Rate Shotgun Rate Deep Passing Rate Rank 27 12 10 2

Three rankings jump out. Keenum is pressured more often than other quarterbacks and when a sack occurs, is sacked the quickest.

Despite that, he passes deep more often than any other quarterback except for Deshaun Watson — even though Keenum didn’t pass deep once in his 20 attempts against the Chicago Bears.

So Keenum has been playing as an aggressive quarterback who doesn’t rely too much on mobility, play-action or seven-step drops to enable a deep passing game. The offensive line isn’t helping him out enough, but his quick decisionmaking has worked for now.

At least, that’s what the statistics say. Throw in his game-to-game volatility, and you get a better read on who he is.

So, in Week 3, Keenum played as one of the best — if not as the singular best — quarterback in the NFL across every game. But he struggled in Week 2 and had an average-to-below-average performance in Week 4. Statistically, his Week 5 performance is quite good, though PFF thinks some additional context puts it in a more mediocre range.

I don’t think anyone would disagree with that, and his volatility is somewhat unique among NFL quarterbacks. Using PFF grade as a proxy, we can figure out how Keenum’s uneven play from week-to-week rates against other quarterbacks.

Using adjusted net yards per attempt, we can look at which quarterbacks have been the most inconsistent players thus far (larger is more volatile, smaller is more consistent):

Keenum hasn’t been the singularly most unpredictable quarterback thus far, but he’s just outside of the top-five.

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He’s performing this well while mostly playing to his scouting report. Here’s what I wrote about Keenum in my 2017 Minnesota Vikings Guide:

Keenum has the makings of a quarterback that will last ten years in the league as a backup who can manage some fundamental skills well enough to create confidence as a stopgap in case of an emergency—the type of quarterback who may be able to win some games with some help and can outperform some of the worst starters in the NFL in any given season.

Strengths: Operates well inside the structure of an offense. Can be aggressive in the right circumstances, though typically cautious. Reads defenses well. Has flashes of brilliance and can explode for production at times. Avoids turnovers. Can throw on the run, creating opportunities for play action and moving coverages.

Weaknesses: Despite ability to avoid turnovers, not particularly accurate and paradoxically poor at short and intermediate passes. Inconsistent. Threw short far too often in 2016, as opposed to a more aggressive playstyle in 2015. Not aware of pressure in the pocket. Cannot improvise when the play breaks down and can run into sacks. For the purposes of a backup in a shotgun-heavy offense, is much poorer at playing from shotgun than under center. A severe lack of arm strength, which means he cannot complete intermediate passes with a modicum of traffic—though doesn’t impact deep ball ability too much.

He has been more aggressive in a Vikings uniform than in a Rams jersey by a substantial margin, but otherwise has been living up to that expectation. He also has avoided turnovers and turnover-worthy throws, showcased mobility and demonstrated more comfort under center — 11.9 yards per attempt and a passer rating of 131.7 — than under shotgun — 6.2 YPA and a rating of 88.3.

If it seems fairly unusual that a college Air Raid quarterback has historically in the NFL — and thus far this season — been better under center than in shotgun… yeah. I don’t have an explanation.

Keenum also has consistently had issues with his worrisome arm strength, though that hasn’t come back to bite the Vikings yet.

We can take a look at some highlight clips that demonstrate his strengths and weaknesses.

The above clip might be Keenum’s best throw. Keenum holds the opposite-hash safety by checking quickly to Stefon Diggs and then slings the ball perfectly in stride to Adam Thielen away from any defenders. With luck, Thielen houses it; either way, a fantastic process for a fantastic result — with pressure coming up the middle.

Those excellent plays don’t happen extraordinarily often. The diagnosis I’ve come across most often for Keenum is a quarterback who often makes the right read but has difficulty placing the ball, keeping it away from defenders or generating enough power to avoid disaster.

In the above clip, Keenum reads the smash combination correctly — something I suspect he may have audibled to given how perfect the call is against a Cover-0 blitz and off coverage.

After making the correct decision, he has difficulty putting the ball in a spot that best helps the receiver. Diggs has to slow up and pluck it away from his frame on a contested catch.

Once again, outside ball placement is a big concern and it’s up to Diggs’ extraordinary capabilities as a receiver to turn an underpowered pass that should have been better contested by cornerback Ryan Smith. You can better see it from the end zone angle below:

Those throws to the outside flagging in the final moments are fairly common:

This time, a defender in zone configuration was better able to locate the pass and contest it.

Keenum also showed a problem in the preseason of leading his receivers into contact. While that hasn’t materialized in a big way in the regular season, there was a throw against the Chicago Bears that was reminiscent of that problem, which you can see below.

It ended up being so poorly placed that it was incomplete (marked as a drop by some grading firms, but the issue is more ball placement than it is receiver error). Had it been complete, Thielen would have been rocked.

Keenum has been more than capable as a backup quarterback. He’s appropriately aggressive, consistently avoids turnovers and often makes the right decision.

To this point, that’s been enough for him to pull together some astounding numbers. Going forward, especially with an injury to Diggs, that likely will not be enough. His ball placement isn’t consistent enough to avoid opposing defenders in traffic, and his velocity isn’t enough to place the ball on outside throws.

When defenses do allow him to throw up the seam, he can create some good opportunities. He also generally does a great job of exploiting defensive mistakes.

The Houston product has been fine in the face of significant pressure and though he doesn’t showcase fantastic capability to elude pressure, his mobility allows him to manipulate defenses on occasion on rollouts and he’s used it to his advantage.

Keenum will regress statistically, and very few people will be surprised to see it happen. But it is demonstrative to see how exactly it could happen and what the benefits to his game are. Not only that, it’s encouraging to see Keenum consistently make smart decisions.

Even with limited capability to hit outside throws and difficulty navigating tight windows, Keenum can use the talented corps around him to keep the Vikings offense afloat. If the Vikings defense can get back to their previous form — which mostly means penalty reduction and some luck with turnovers — then the Vikings can stay on a tenuous path to the playoffs.