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-one at the opposing team’s goal line, the model will predict an expected points value near seven; 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.
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:
Chiefs vs Colts, October 6
The Chiefs and Colts battled back and forth until midway through the third quarter, when the Chiefs’ offense stalled in Colts territory thanks to a few costly penalties. From there, the Colts slowly ran out both the clock and with it, the Chiefs’ chances of a comeback. As always, I’ve noted the five plays with the biggest impact on the game:
This is the second week in a row that Byron Pringle has been heavily featured on this chart. As teams look to double-cover the Chiefs’ top receiving threats, Mahomes seems to be able to consistently rely on his WR3 and WR4 to make plays. But his wasn’t quite enough last week.
Meaningfully analyzing Mahomes’ performance this week is tough. There is nothing in the advanced metrics available to us that can capture a player trudging through an injury, and unfortunately, there is no stat for how many times his linemen found themselves butt to grass. That said, here’s what the stats show:
A quick note on this chart: if you’ve been following this column, you may notice Mahomes’ 2018 average and a few other numbers appear a bit different this week. That’s intentional. I’ve changed the calculation slightly so that on pass plays with wide receiver or running back fumbles — such as the one LeSean McCoy had on Sunday — the quarterback’s EPA is not hurt. Instead, the quarterback gets credit for the EPA gained at the point of catch on those plays, ignoring what happens afterward. This isn’t a perfect solution but helps big fumbles (which aren’t the fault of the quarterback and are rare occurrences) from skewing the data.
Mahomes was not himself this week.
There are a multitude of factors that affected his performance (injuries, drops, bad protection). But the important thing to note here is that even with all of that, he managed to put up positive EPA per play and almost an “average” performance for an NFL quarterback in 2019. Now, does any Chiefs’ fan want Mahomes to be average? Of course not. But this was the worst game of the young QB’s career, and if his absolute floor as a player is just “average,” the Chiefs’ offense is in the right hands.
Let’s take a look at the depth of Mahomes’ targets:
Despite having less-than-ideal protection, Mahomes actually distributed his passes slightly deeper than in Weeks 1-4.
The cost of holding on to the ball to air it out? He took a lot of sacks.
This chart shows the total number of quarterback hits Mahomes has taken each week in the faded bars, with the number of sacks in the opaque bars. Not only was he hit seven times (and this number could be low, as some hits are not registered on the official stats), but the Colts were also able to make four of those hits before Mahomes had a chance to release the ball.
Here’s what is interesting to me:
In Week 1 against the Jaguars, Mahomes hurt his ankle.
Andy Reid responded by scheming up shorter passes, and Mahomes got rid of the ball quicker (an average of 2.42 seconds, the fifth-fastest of quarterbacks that week — data courtesy of Next Gen Stats). This really helped limit the influence of Mahomes’ limited mobility and allowed the Chiefs’ offense to continue to be very efficient.
Against the Colts, the story was different. Not only did Mahomes continue to look for deep shots, but he also didn’t shorten his release time — getting rid of the ball an average of 3.07 seconds after the snap, the sixth-slowest of quarterbacks in Week 5.
I am absolutely no football coach — I’m just a guy who codes and crunches numbers. But it will be interesting to see what Reid draws up to keep this offense moving with Mahomes likely to be hobbled the next few weeks.
Now, one thing readers have been asking for is more data comparing the Chiefs’ performance to the rest of the league. Today, your comments have been answered.
Here’s a table of all quarterback performances for Week 5:
QB Performance - Week 5
|Passer||EPA/Play||ADoT||Cmp Rate||QBHit Rate||QBSack Rate|
Chiefs receiving corps
On to the pass-catchers.
Once again, the Chiefs really struggled to add much after the catch — with the exception of LeSean McCoy, though those yards were immediately followed by a fumble. Reid has not done as good a job at getting his receivers into space against these recent man coverages as he has against zone.
Which wide receivers were the most efficient, and how does this compare to the rest of the league?
Hardman and Pringle made the most of their targets, averaging around 0.75 expected points added with each target. McCoy is down near the bottom of the league thanks to his fumble, while Kelce and Robinson are probably lower than you may have expected.
The Chiefs actually lost expected points (they put themselves in a less likely position to score) on average when targeting Demarcus Robinson. Kelce, on the other hand, had a positive EPA, but he was just about average compared to the rest of the league. Kelce is certainly not an average player, but he had a few drops Sunday, which prevented him from being too efficient.
The gap between arguably the Chiefs third and fourth receiving options (Hardman and Pringle) compared to their first and second (Kelce and Robinson, w/out Hill and Watkins) is quite significant. Why is that?
Well, for that, I again went to the tracking data from Next Gen Stats. Kelce and Robinson simply couldn’t get much separation. On average, at the time of target, Kelce only had two yards of separation (ranked 48th of 56 receivers with five or more targets) while Robinson had 1.9 (50th of 56). In contrast, Pringle and Hardman had 4.1 (4th) and 4.0 (7th) average yards of separation, respectively. When the defense focuses on taking away Kelce and Robinson, they don’t seem to be able to consistently beat their coverage lately — unlike Hill and Watkins.
Chiefs rushing attack
Let’s see how the Chiefs’ running game fared, depending on which gap they attacked:
The Chiefs only ran the ball 11 times against the Colts. And, only four of those runs were successful — which happened to be straight up the middle or behind the guards. You’ll notice the runs to outside of the tackles, or the C-gap are missing from this chart — that’s because there were none this week, only runs to the A, B and D-gaps.
Some fans were hoping Reid would run the ball more as the game progressed, but when you’re only achieving a successful play on ~36% of your runs, it’s probably best he abandoned it.
There isn’t much point in including the usual table comparing running backs this week. Damien Williams was the only player with more than one carry, and he averaged a horrific -0.46 Expected Points per Carry. What that means is with every handoff to Damien Williams, the Chiefs’ essentially lost half a point.
With nine carries, that means Damien Williams cost the Chiefs a little over four points, in a game only decided by six. Yikes. Of all running backs with five carries in Week 5, that puts Damien Williams as the 51st back of 54 in EPA/carry.
The other two carries belonged to Anthony Sherman, who converted a fourth down for 1.6 EPA, and Hardman, who lost almost an entire expected point on his lone carry.
With five weeks of football played, what does the Chiefs’ rushing attack look like?
You’ll notice a few things.
First, they have overwhelmingly ran the ball to the middle of the line. And second, running to the middle and right has been more successful than to the left on average. Third, no gap has better than a 42% success rate — meaning running the ball is not an efficient use of a play-call for the Chiefs on average.
Thankfully, that hasn’t been the play-call that often.
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 had their highest pass-run ratio of the 2019 season this week, passing the ball 81.5% of the time in neutral game-script situations. This led the league by a wide margin in Week 5 — only the Patriots and the Packers had over 70%.
Moving on to the other side of the ball, let’s see how the pass and run defenses compared.
Chiefs Defense vs Colts
|Play Type||EPA/Play||Success |
Despite what it may have felt like, the Colts actually ran a fairly balanced attack (though in today’s NFL, a “balanced” attack typically consists of more passes to runs).
Without Tyrann Mathieu’s interception of Jacoby Brissett, the efficiency of the Colts run and pass would look very similar. Both were successful just over 50% of the time.
As the run defense was the topic of many conversations following the loss, let’s look at just where the Colts attacked.
This is not a pretty chart for the Chiefs (unless you really like the color blue). The Colts were quite successful running the ball, particularly to the right side. A large majority of their runs were to the middle, which the Chiefs actually did a decent job at stopping.
How does this compare to the Chiefs’ run defense throughout the season so far?
Here, we see the dramatic difference between the left and right sides (from the perspective of the offense) of the run defense for Kansas City. Opponents have ran more often and been more successful when running to the right.
With the news of the recent Chris Jones injury, it’s unlikely this run defense will improve anytime soon. However, excluding fumbles (to fairly evaluate the defense without including Brashaud Breeland’s 100-yard return), the Chiefs’ run defense is actually only sixth-worst in the league in EPA per play. While this isn’t great, run defense just isn’t as important when it comes to predicting a teams’ win total. But more on that at a later time.
That’s it for Week 5 of Stacking the Box Score.
Leave a comment or reach out on Twitter (@ChiefsAnalytics) if you have questions or would like to see something new for next week. Thanks!