Nick Mullens was an undrafted free agent who was signed by the 49ers last year, but he never made it to the club’s official roster for the 2017 season. He was cut before the start of the 2017 season , and then cut again before the start of the 2018 season. Then, after Jimmy Garoppolo tore his ACL, the 49ers brought Mullens up to the active roster. He sat behind C.J. Beathard until a wrist injury knocked him out of the lineup, vaulting Mullens into an unlikely starting role. Since then, he’s been a remarkable find: you would expect an undrafted free agent to operate at replacement level, but Mullens has actually been an above-average starting quarterback.

And he’s been the best rookie quarterback this season, in a year where five first round quarterbacks are playing. Your first question might be: is Mullens actually a rookie? The answer is clearly yes: he is on a contract that pays $480,000 per year, which is the rookie minimum; if he was treated as a second-year player, the CBA would mandate that he receive no less than $555,000 this season. Instead he is on a contract that mirrors what 2018 UDFA rookies are seeing. He’s also the same age as Baker Mayfield; both graduated from high school in 2013 and played four years in college; the difference is Mullens graduated in ’17 and was on a practice squad last year, while Mayfield transferred in 2014 and sat out that season. But since Mullens wasn’t on an active roster last year, this is obviously his first season in the NFL, which I think makes him a rookie for just about every purpose.

The table below shows the passing stats from Mullens and the five rookie first round picks this year. Mullens has been the best of the bunch in terms of both passing yards per game and ANY/A.

Game Game Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Rush Rush Rush Rush Rush Rk Player Age Draft Tm G GS Cmp Att Cmp% Yds TD Int TD% Int% Rate Sk Yds Y/A ANY/A Y/G W L Att Yds Y/A TD Y/G 1 Nick Mullens 23 SFO 6 6 131 203 64.53 1754 10 6 4.9 2.96 96.0 13 100 8.64 7.33 292.3 3 3 17 -14 -0.82 0 -2.3 2 Baker Mayfield 23 1-1 CLE 12 11 260 407 63.88 3065 21 11 5.2 2.70 92.6 25 173 7.53 6.52 255.4 5 6 33 115 3.48 0 9.6 3 Lamar Jackson 21 1-32 BAL 14 5 73 124 58.87 818 5 3 4 2.42 82.0 11 57 6.60 5.38 58.4 4 1 114 566 4.96 3 40.4 4 Sam Darnold 21 1-3 NYJ 11 11 199 351 56.70 2357 14 15 4 4.27 72.8 24 154 6.72 4.82 214.3 4 7 40 106 2.65 1 9.6 5 Josh Allen 22 1-7 BUF 10 9 132 253 52.17 1633 6 9 2.4 3.56 65.5 27 204 6.45 4.09 163.3 4 5 75 506 6.75 6 50.6 6 Josh Rosen 21 1-10 ARI 12 11 187 336 55.65 2042 10 14 3 4.17 66.3 35 261 6.08 3.64 170.2 3 8 19 89 4.68 0 7.4 View Original Table Provided by Pro-Football-Reference.com

What’s most remarkable about Mullens is his 8.6 yards/attempt average. Ignore the fact that he’s a rookie: only three players in history have averaged 8.6 yards/attempt at 23 years of age or younger: Ben Roethlisberger, Dan Marino, and Y.A. Tittle. Patrick Mahomes is likely to join them this year, and Mullens may, too. In fact, 23-year-old Deshaun Watson is right behind him at 8.4. But that almost operates as a positive for Mullens: it’s remarkable company, and a reminder that he’s 4th in the NFL this season in yards/attempt.

And while you might want to credit Kyle Shanahan for most of the success, that seems unfair to Mullens. For starters, look at how all 49ers quarterbacks have done in two years under Shanahan: Mullens stands out as nearly as good as Garoppolo last year, which was considered a performance worthy of a mega contract:

Query Results Table Game Game Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Rk Player Year Age Draft Tm G GS Cmp Att Cmp% Yds TD Int TD% Int% Rate Sk Yds Y/A ANY/A Y/G W L 1 Jimmy Garoppolo 2017 26 2-62 SFO 6 5 120 178 67.42 1560 7 5 3.9 2.81 96.2 8 57 8.76 7.62 260.0 5 0 2 Nick Mullens 2018 23 SFO 6 6 131 203 64.53 1754 10 6 4.9 2.96 96.0 13 100 8.64 7.33 292.3 3 3 3 Jimmy Garoppolo 2018 27 2-62 SFO 3 3 53 89 59.55 718 5 3 5.6 3.37 90.0 13 97 8.07 5.75 239.3 1 2 4 C.J. Beathard 2018 25 3-104 SFO 6 5 102 169 60.36 1252 8 7 4.7 4.14 81.8 18 156 7.41 5.03 208.7 0 5 5 Brian Hoyer 2017 32 SFO 6 6 119 205 58.05 1245 4 4 2 1.95 74.1 16 112 6.07 4.67 207.5 0 6 6 C.J. Beathard 2017 24 3-104 SFO 7 5 123 224 54.91 1430 4 6 1.8 2.68 69.2 19 141 6.38 4.52 204.3 1 4 View Original Table Provided by Pro-Football-Reference.com

And who is Mullens throwing to? TE George Kittle (2017 5th round pick, albeit one who appears to be a star), WR Dante Pettis (2018 2nd round pick), RB Matt Breida (2017 UDFA), and WR Kendrick Bourne (2017 UDFA) are his top four receivers. That is a below-average supporting cast by any measure. Say what you may think about Shanahan, but even if you want to argue that Mullens has a better infrastructure/supporting cast than most of the 2018 rookies, it’s still a below-average one, and the difference between Mullens’ performance and the average rookie performance is much larger than the difference in their supporting casts.

And let’s not forget that he’s an undrafted rookie free agent. If you could get top-10 QB numbers (he currently ranks 9th in ANY/A) from a UDFA by putting him on a team with a great offensive coach and a bunch of low-profile rookies and second year players, then NFL teams are really missing the boat on quarterback evaluations.

That said, there is a key difference between past production and future performance, and it’s fair to be skeptical as to whether Mullens’s success will continue. The biggest red flag? On his average completed pass, 7.53 of Mullens’s passing yards have come after the catch, and just 5.86 before the catch. Mullens ranks 1st by a mile in YAC per completion, and 22nd in air yards per completion. So his performance may not reflect him as much as his teammates or just plain old variance on small sample sizes. Mullens has 5 completions of 50+ yards and 3 of 70+ yards, and four of those five were short passes. That’s not sustainable and it is obviously inflating his yards/attempt and ANY/A numbers.

So it may not last for long: but for now, Mullens has been the most effective rookie quarterback in the NFL. And that’s an amazing story.