Welcome to this week’s Stacking the Box Score, where I’ll be quantifying what went down between the Kansas City Chiefs and their most recent opponent — in this case, the Oakland Raiders, whom the Chiefs defeated 40-9.
As always, here’s a quick primer on some of the stats and data I’ll be using. If you already feel comfortable with these metrics, skip the link and keep reading!
Chiefs vs. Oakland Raiders, December 1st
It seems like Chiefs games have gone one of two ways this season: they’re over by halftime, or they’re in constant flux until the last play. This game was one of the former — which we clearly see when we look at win probability throughout the game.
There were three plays in this game that had huge impacts.
One was Rashad Fenton’s forced fumble on a Raiders kick return. It was the biggest win probability swing of the game — and the second consecutive game in which Fenton has been on this list due to a turnover. The other two were costly mistakes by Derek Carr — and great plays by Kansas City safeties: a pick-six from rookie Juan Thornhill, and an interception by free-agent addition Tyrann Mathieu.
This lines up with what we saw during the game; while the offense did enough to win, it was the defense and special teams that really swung the pendulum toward the Chiefs.
On the surface, the Chiefs were very efficient when choosing to pass — eclipsing Mahomes’ league-leading 2018 numbers. But this may not have been just because of Mahomes’ passing excellence. Let’s break this down further.
Here we’re charting EPA for all plays in which the Chiefs chose to pass for each week of the season. This means that Mahomes (or Matt Moore) gets credit for defensive penalties such as roughing the passer — along with plays like Mahomes’ touchdown scramble on Sunday. These plays positively influence games and should be captured — that’s why ESPN’s Total Quarterback Rating (QBR) includes them; they measure how much a QB contributed to the win.
But what if we just look at Mahomes’ EPA on plays where he actually threw the ball (excluding penalties, sacks, and scrambles), and compare his efficiency and accuracy (adjusted for target depth) to the rest of the league this week?
Mahomes finds himself next to Drew Brees, Tom Brady, and... Andy Dalton?
It wasn’t a great week for the league’s star quarterbacks — and Mahomes was no exception. Mahomes’ depth-adjusted completion percentage (or CPOE) was seventh-worst in the league in Week 13 — and far worse than his opponent Derek Carr.
Carr has actually been one of the more accurate passers in the league this year, so his position on the right side of this graph isn’t totally unsurprising. However, his two costly interceptions lowered his EPA per pass well below Mahomes — and the majority of the league.
What led to Mahomes’ low CPOE? Inaccuracy (or at least not connecting) on the deep ball. Despite attempting six of them, Mahomes only completed one pass past 15 yards. Could this have been a protection issue — that is, Mahomes didn’t have the time to make accurate throws?
This chart shows us that the offensive line kept Mahomes from being hit as well as any other week this season. But it also shows us the limitations of public data.
With only hits and sacks at our disposal, we don’t know how many of Mahomes’ passes were hurried — but from watching the film, we know that quite a few were.
So maybe these low hit and sack numbers don’t represent the offensive line returning to form, but rather that Mahomes’ ankle is no longer limiting his mobility, allowing him to better escape pressure and get rid of the ball — even if the throw ends up being rushed. With the available data, we can’t know for sure — but the film points to the latter.
Is this issue with connecting on intermediate-to-long depth passes a real trend or just a one week blip? Let’s compare his accuracy in this range to 2018.
When we look at Mahomes’ completion percentage as a function of the depth of target, we see that once we get to about 10 yards down the field, there is a clear difference between last season and this one.
In the 10-20 yard range, Mahomes and his receivers have been less deadly this year than last. In fact, Mahomes has only completed around 40% of passes he’s thrown 15-20 yards in the air this season — compared to 60% in 2018. Should we be worried?
Well, Mahomes is still the second-most efficient passer by EPA per dropback in 2019 — just behind Baltimore Ravens quarterback Lamar Jackson. So this hasn’t greatly limited the Chiefs’ passing efficiency.
In fact, the optimistic take would be that this season’s dip in intermediate-to-long range success is a positive thing. Mahomes is likely well above an average quarterback at this range, but right now, he’s completing passes below the NFL’s average level. If that swings back to the league average, we could see the Chiefs passing offense take an additional step forward — which could take them from being a Super Bowl contender to a Super Bowl favorite.