Against the Texans in the Division Round of the 2019 postseason, Mahomes gained 16 passing first downs on 35 passes (no sacks), for a remarkable 45.7% passing first down rate. The Chiefs receivers also had six drops in this game and Mahomes picked up a first down on all four of his scrambles: this means he gained 20 first downs on his 33 plays where a receiver didn’t drop a target: it was truly a magical performance by Mahomes.

Against the Titans in the 2019 AFC Championship Game, Patrick Mahomes threw for 14 first downs on 35 passes, while also taking two sacks. That’s a passing first down rate of 37.8%. Note that this ignores that Mahomes scrambled 6 times and picked up a first down on four of them, so his true first down rate was 41.9% (the Chiefs also just dropped two passes here).

Let’s ignore the advanced stats for a minute (scrambles, drops) and just focus on his passing numbers: Mahomes has picked up 30 first downs through the air on 72 dropbacks this postseason, a 42% rate. That’s amazing, but it isn’t as amazing the standard way we analyze quarterbacks here: Mahomes is averaging 10.74 ANY/A this postseason!

During the regular season, Mahomes was a bit worse than you would expect when it comes to passing first down rate. In the 2018 regular season, Mahomes had a 39.1% passing first down rate: while that is excellent, it placed him 3rd in the NFL and not far ahead of 5th (38.9%); meanwhile, his ANY/A (8.89) was the best in the league, and far ahead of everyone other than Drew Brees. And during the 2019 regular season, the disparity between his ANY/A and his passing first down rate increased. While Mahomes ranked 2nd in ANY/A, he “only” ranked 11th in passing first down rate.

In fact, he finished the regular season a hair behind Kyle Allen (who ranked last in ANY/A) in this statistic, a shocking development that we looked at back in mid-December. So we are seeing a bit of a trend that Mahomes tends to fare better in ANY/A than passing first down rate, and that’s even continuing in the 2019 postseason (again, if you ignore his 8 scrambles for first downs, which is an outlier: in 31 regular season starts, he’s rushed for just 37 first downs).

So I wanted to investigate, because both ANY/A and passing 1st down rate are excellent measures of quarterback play. And we know Mahomes is a phenomenal quarterback, so him faring relatively — and relative is the key word here — poorly in passing 1st down rate is interesting. So what’s going on?

1) Mahomes has an outstanding interception rate. When it comes to ANY/A, throwing interceptions matter; when it comes to passing first down rate, all incompletions are treated equally as failed first downs. Mahomes has thrown just 5 interceptions on 554 pass attempts this season, including the playoffs. The Tampa Bay quarterbacks (Ryan Fitzpatrick in 2018, Jameis Winston in 2018 and 2019) and the San Francisco quarterbacks (Nick Mullens in 2018, Jimmy Garoppolo in 2019) have had good passing first down rate numbers the last two seasons, but higher than average interception rates. One reason Mahomes is arguably the best quarterback in the NFL is because he is great at avoiding turnovers, and passing 1st down rate ignores that trait.

2) Mahomes does not take many sacks, which is great for his ANY/A (and his real life team!) but not necessarily all that helpful for his passing first down rate. Mahomes may throw it away, or throw it in the general vicinity of a covered receiver on plays where other quarterbacks would take a sack. (surprisingly, Mahomes’ bad throw percentage is above average, which indicates perhaps he is doing this). A sack and an incompletion are treated the same in P1D%, but the former is better in ANY/A.

3) Mahomes doesn’t get many “easy” first down opportunities. The Chiefs have been pretty run-heavy on 3rd-and-1, and only 3 of his first downs all season came on 3rd-and-1.

4) Big plays. During the regular season, 5.4% of his dropbacks ended with a 30+ yard pass completion, the highest rate in the NFL. Even if you ignore sacks and incomplete passes, 8.5% of Mahomes’ completions went for 30+ yards, also the highest rate in the league. That helps a player’s ANY/A, but those excess yards after picking up a first down don’t help your passing first down rate. Last year, Mahomes led the NFL in 30+ yard passes with 33, so this is just part of his game (which is also obvious to anyone who watches Mahomes).

So, in conclusion: Mahomes is awesome. He manages to avoid bad plays *and* make a ton of big plays while also having a very good (if not outstanding) first down rate. None of this is breaking news, but I thought more investigation was warranted.

What do you think?