Nick Mullens: PACR hero

Nick Mullens’ first six games have been remarkable. The 49ers were the only team to give him a pre-draft visit, and now the undrafted free agent is outplaying many quarterbacks who heard their name called on draft weekend. Mullens’ 49ers have a 3-3 record since taking over — including their first win against Seattle in five years. His 1,754 yards are the fourth most in NFL history for a quarterback’s first six starts. The simple fact that Mullens is on the same list as Cam Newton, Marc Bulger, Patrick Mahomes, and Andrew Luck is insane.

Mullens’ underdog story is fueled by his ability to diagnose defenses and release the ball quickly. When throwing the ball in under 2.5 seconds, his 115.7 quarterback rating is tied for 11th in the league with Tom Brady. Perhaps his best throw of the year highlights why he’s been able to find early success. Late in the Week 15 game against Seattle, he diagnoses man coverage based on pre-snap shifts. He takes the information, confirms post snap, and throws with impressive anticipation.

His processing and release are also apparent against the blitz. Through Week 15, defenses blitzed Mullens 59 times. On those plays, Mullens has an adjusted completion percentage of 78.7, a gaudy 9.7 yards per attempt, five touchdowns, one interception, and a quarterback rating of 113.8.

Mullens is playing well, but the secret recipe to his success may be one part Mullens and two parts Kyle Shanahan. Passing Air Conversion Ratio, or PACR, is an efficiency metric created by Josh Hermsmeyer. It measures the rate at which a yard thrownthrough the air is converted into an actual receiving yard. The formula for PACR is simple: Passing yards divided by air yards. A PACR of 1.0 indicates that as soon as a receiver caught the ball he is stopped without gaining another yard. The higher the PACR ratio, the more a quarterback’s yards consist of yards after the catch.

Eric Eager, data scientist at Pro Football Focus, plotted a raw PFF grade against PACR to get a sense of the relationship between throw by throw performance and PACR. Nick Mullens is, as the statisticians would say, an outlier.

The chart really says more about Shanahan than it does Mullens. Mullens being so high on the PACR axis means his passing yards consist of a lot of yards gained after the catch. Shanahan schemes receivers open with a regularity typically reserved for clocks. Since Week 9, Mullens is tied for fifth-most most open throws in the NFL per PFF. And he has the third-most open throws to his first look. Mullens is executing within the structure of the offense, and his statistical line reaps the rewards.

Scheming wide receivers open is one part of the equation, but Mullens also benefits from the NFL’s newest break out star tight end. George Kittle’s 747 yards after the catch through Week 15 is second in the NFL. Every other player in the top-nine is a running back, which makes sense given the position feasts on dump-offs. The closest receiver on the list? JuJu Smith-Schuster at 10th. Smith-Schuster could catch a one yard pass and take it 99 yards to the house in each of the final two games and still not have as many yards after the catch as Kittle.

Mullens has clearly outplayed walking bag-o-grit C.J. Beathard. Keep in mind that Beathard is still pretty high on the PACR axis, further indicating the structure of Shanahan’s offense has a hand in Mullens’ yardage. This isn’t a knock on Mullens as much as it is recognition that he can operate well within the structure of the offense. Brian Hoyer would tell you this isn’t a given, but at the same time it’s important to contextualize the performance.

The creator of PACR said it best:

Mullens is performing well because he’s able to perform what Shanahan asks of him. And at minimum, that’s a fantastic skill for a backup quarterback.