Chiefs-Texans: Stacking the Box Score for Week 6

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.

As always, here’s a quick primer on some of the stats and data I’ll be using this week (feel free to skip this part if you’ve read this column before):

Expected points added (or EPA)

EPA is a metric showing how many expected points a team added on a given play.

Here’s the short version: it captures the true value of a play by accounting for the context in which it occurred.

The longer version?

EPA is calculated by first determining how likely the next score of the game is — a touchdown, field goal or safety — based on a variety of factors that include field position, down, yards-to-go, score differential and time remaining in the game.

More precisely, if a team is first-and-1 at the opposing team’s goal line, the model will predict an expected points value near 7; it’s very likely that the team will score a touchdown. So if a player in that situation then runs the ball in for a touchdown, the expected points added (EPA) won’t be very large.

On the other hand, if a team is at fourth-and-19 at their own 20-yard line, there could be negative expected points in that situation; it’s more likely the other team will score next. So if a quarterback throws a deep bomb for a touchdown, that play will have a very high EPA value.

Success rate

A play is a success if it had a positive EPA value. So if a team has a 60% success rate, that means 60% of their plays had a positive EPA. A run of two yards on first-and-10 is often not a success; a team tends to be less likely to score after such a play.

Average depth of target

This metric quantifies how far a quarterback’s average pass is thrown down the field. It is measured vertically (straight north/south) from the line of scrimmage to where the receiver catches (or doesn’t catch) the ball. Obvious throwaways are recorded as 0 air yards, to prevent a QB from gaining credit for just throwing the ball out of bounds 20 yards downfield. This metric is a useful way to quantify and compare the gunslingers against the check-down artists.

Win probability model

There’s something very important to note about the win probability model I will be using for this series. It does not take into account the strength of either team in the match-up. Both teams begin the game with a 50% to win. All the model is doing is looking back over the past decade to say historically, given the current score, possession, time remaining, home-field, etc., how often has this team ended up winning. If you want to see an actual look at how likely the Chiefs are to win the game, just check the vegas odds before the game and at halftime.

So, if this model does not perfectly predict who will win, what good is it? Well, it’s an excellent way to contextualize just how important a play was. We can say that before Mahomes did _________, the Chiefs had a 30% chance of winning, and after, they had a 70% chance. Thus, we can say that the amazing thing Mahomes just did added 40% to the Chiefs win probability — also known as Win Probability Added. This makes our model very useful because it treats all teams equally and thus lets us compare plays across games to see which had the biggest influence on the game.

Now that that’s out of the way, let’s get to analyzing Sunday’s game:

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Chiefs vs. Houston Texans, October 13

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Win probability

Like last week’s game — and similar to every loss of Patrick Mahomes’ NFL career — a Chiefs victory was never truly out of reach until the very end.

A couple of plays jump out to me from this graph.

First, the strip-sack of Mahomes (and the recovery by Benardrick McKinney) was a huge swing in win probability — the largest of the game.

Second, the 68-yard punt by Dustin Colquitt was a net gain of around 12% win probability for the Chiefs. Of course, this isn’t to say it was better for the Chiefs to punt than to avoid a fourth down. But given the situation the Chiefs were in, Colquitt’s booming punt did 12% more for the Chiefs’ win probability than an average NFL punt.

Getting into that fourth down dipped the Chiefs’ chances at winning the game to below 50%, but flipping the field position as well as Colquitt did increased them back to 60%. Unfortunately, this didn’t prevent Deshaun Watson and the Texans from driving down the field and securing the victory.

Patrick Mahomes

Here is Mahomes’ weekly EPA per play performance chart.

Mahomes was efficient passing the ball on Sunday. If you ignore his fumble, his 0.26 EPA per play ranked ninth among quarterbacks this week — excluding the Monday night game, which at this writing has yet to be played. Including the fumble, he was still above average, but drops to the 13th best QB this week.

What drove this increase in passing efficiency compared to Week 4 and Week 5?

Something I pointed to in last week’s column: Mahomes had shorter passes and got rid of the ball faster.

According to Next Gen Stats, Mahomes got rid of the ball in an average of 2.77 seconds last week. While this number is right around average for the league in Week 6, it was 0.3 seconds faster than his time to throw in Week 5 against the Indianapolis Colts.

As you can see here, this led to a higher proportion of Mahomes’ passes being in the range under 10 yards — and a lower proportion on the 10 to 30-yard range.

And it had another positive effect: fewer hits and sacks.

The Chiefs offensive line drew a difficult assignment against the Texans, lining up against a Houston defensive line featuring J.J. Watt — the league’s second-best pass rusher, according to ESPN’s Pass Rush Win Rate metric — and as a group, boasting the 10th-best pass rush win rate.

But probably because of his faster release time, according to NFL’s official stats, Mahomes took two only quarterback hits on Sunday. It is possible that one of these hits led to Mahomes re-aggravating his ankle injury — and the other hit was the sack that forced a fumble and led to the Texans scoring a touchdown on the next play. So regardless of its limited production, the Texans defensive line had a big impact on the game.

For comparison, here’s the performance of all quarterbacks who registered at least 10 passing attempts on Sunday.

Chiefs receiving corps

Against Houston — for the first time since Week 1 — the Chiefs were able to gain a majority of their receiving yards after the catch.

Hitting Travis Kelce, Mecole Hardman, Byron Pringle, Damien Williams and Darrel Williams in stride — and in space — allowed their athletic ability to shine; the Chiefs’ passing attack benefited as a result.

While many view Tyreek Hill as a receiver who gets lots of yards after the catch, since 2018, a smaller proportion of his receiving yards have come after the catch — at least when compared to Kelce, Sammy Watkins or any of the Chiefs’ running backs. This isn’t to say that Hill doesn’t make guys miss and gain yards after the catch. Instead, it demonstrates what we saw on Sunday: a lot of his catches are in (or near) the end zone, where there aren’t many (if any) yards to be gained.

Where were these receivers targeted — and how efficient were the targets?

As a reminder, any player above the red line means that targeting that player was good for the offense on average, while the players more to the right side of the graph were targeted on deeper routes.

Both Demarcus Robinson and Hill had some of the higher average depth of target in the league in Sunday — but of the two, only Hill was effective with those targets; Robinson failed to pull in any of his four targets.

Chiefs rushing attack

At this point, calling the Chiefs’ running game an attack feels a bit... oxymoronic.

In fact, the Chiefs ran the ball so few times against Houston that it would be irresponsible to break down the effectiveness of these runs by location because of the limited sample size. So instead, here’s an updated graph of the Chiefs rushing offense by location through the first six weeks of the season.

Chiefs play-calling

When analyzing a team’s play-calling tendencies, it is important to separate early-down, neutral game-script plays from the rest of the game. Why? Well, any team that is winning by a significant margin is going to run the clock out, and any team that is way behind is going to pass. Furthermore, third and fourth-down play-calling is largely dictated by the yards needed to gain the first down.

So instead of looking at run-versus-pass percentages over the course of the whole game, we only look at first and second down, when the Chiefs’ win probability was between 20% and 80%.

The Chiefs again had their highest pass-run ratio of the season against the Texans, passing the ball 85.7% of the time in neutral game-script situations. This is the highest neutral passing percentage of any team in any game this season.

But here’s what’s frustrating — and concerning — about the play-calling on Sunday: despite passing at a league-high rate, they ran the ball on second-and-14 in the fourth quarter. Neither that play (or the series) were successful. The Chiefs ended up punting the ball two plays later, never getting another chance on offense.

Just how bad was this call?

Well, since 2018 the Chiefs have run the ball 13 times on second-and-long — that is, with 10 or more yards to go. Not a single one of these plays have been successful — that is, leaving the Chiefs more likely to score than they were before the play was run.

Further, in 2019, the Chiefs have converted just 30% of the series in which they’ve run the ball on second-and-long — compared to 73% of the series in which they’ve passed the ball on second-and-long. (In this case, converting meaning getting a new set of downs or a touchdown on that play or on third or fourth down).

This split is far greater than the rest of the league this season. Other teams have converted 40% of series in which they’ve run on second-and-long and only 54% when they’ve passed.

In other words, when you have a quarterback who is as effective at moving the ball through the air as Mahomes is, you should pass the ball on second-and-long — especially when that play is during your team’s last chance at winning the football game.

Chiefs defense

In the past few weeks, there has been a lot of talk about the Chiefs defense — and look, I get it: the Chiefs defense has been bad. It’s sometimes been very bad.

But one opinion that is often presented with far more tenacity than evidence is that the Chiefs run defense is the sole problem with the unit — and if it were better, the team wouldn’t be losing these games.

I’m here to argue that not only is the run defense not as big of a problem as many claim but also that if the Texans had run less (and thus passed more), the Chiefs could have lost by even more on Sunday.

This graph compares the EPA (both total and per-play) by play type for the Texans offense against the Chiefs defense. On average, the Texans’ gained 0.35 EPA per dropback, while they gained -0.02 EPA (that is, they lost EPA) per run.

Some have made the (largely nonsensical) point that the Chiefs’ opponents aren’t actually trying to score — they are instead trying to control the clock, keeping the ball away from Mahomes. I’ve already explained how time of possession, in itself, does not win football games — other than on a team’s last drive.

But let’s assume that this premise is true. Teams are not trying to score points against the Chiefs any longer. They just want to keep Mahomes from having the ball. It is correct that this would not be captured in the Expected Points model, which is a measure of a team’s likelihood of scoring; if the team isn’t trying to score, the model does not represent the team’s success.

Thankfully, we have another tool at our disposal: Win Probability Added (WPA). This model considers factors such as time left in the game, time outs remaining and score differential to account for situations where running the ball may not increase the teams’ likelihood of scoring, but does increase their probability of winning.

Here’s how WPA looked for the Texans when broken out by play type.

When the Texans passed the ball, they increased their team’s chance of winning the game by four times as much as they did when they ran the ball. In total, they added 70% to their win probability through the air, and only 10% on the ground.

Even if we concede that time of possession is what wins football games, the best way to increase time of possession is to maintain possession by converting first downs. The Texans converted on 44% of their passes, but only on a third of their runs.

Others have argued that it is the first down runs that were the problem against the Texans, as those consistently gained 4-5 yards and put the Texans in a good position to convert through the air. But even just looking at early-down plays, the Texans were successful (put their team in a better chance to score) on 55% of early-down passes, and only 45% of early-down runs.

No matter which way you slice it, the Texans had more success through the air than on the ground.

As far as evaluating the Chiefs defense goes, the difference may not matter. As it turns out, the worst performers against the pass for the Chiefs were the linebackers; Chiefs fans can likely agree that this position group needs to improve in all aspects

That said, where did the Texans run game succeed against the Chiefs?

And, how do these numbers compare to the season so far?

Teams definitely seem to be targeting the right side of the field with runs more often — and winning there more consistently.

Chiefs special teams

One aspect of the Chiefs’ performance I have yet to analyze in this column is the special teams unit. This is largely because of the way play-by-play data is available from NFL.com; special teams play is simply difficult to analyze.

But after six weeks, there is an alarming trend for the Chiefs on special teams. The Chiefs are averaging a penalty on one of every five kick or punt returns this year. That’s more than 28 other NFL football teams. That’s very ungood — especially for a unit that used to be considered one of the best in the league.

Against the Texans on Sunday, this number was even higher — averaging a penalty on 40% of special teams returns. Given the Chiefs’ struggles in other areas of the game, this number has to go down.

That’s it for Week 6 of Stacking the Box Score.

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