Applied NFL Analytics: Mahomes, Offense Got Better After The Bye Week

The Passing Touchdown Improvement Index is, like any index, a measure of health in a particular market. Think the NASDAQ in the stock market. This index measures a quarterback’s health, and that of the passing offense as a whole, by measuring his propensity to throw touchdowns instead of interceptions, and the rate of change in that propensity week to week.

Keeping in practice with the first law of football behavior, the quarterback is driver of the offense, touching the ball every single play, holding the most weight in their ability score points within the time they possess the ball.

Throwing touchdowns is the most direct way for the quarterback to contribute to the offense’s primary responsibility of scoring points with the opportunities they have. Whereas throwing interceptions, whether his fault or not, is the most direct way for an offense to lose opportunities too score points involving the quarterback.

Reminder: touchdowns and interceptions are multi-player stats. Someone has to throw it, and someone has to catch it. Receivers can run wrong routes, deflect passes to defenders, etc. This is truly a measure of team passing offense, led by the quarterback, who has the most weighted value in the equation, though NOT THE ONLY value in the equation.

The Passing Touchdown Improvement Index is measured by looking at Passing Touchdown Behavior Rate (rate of passing touchdown celeration) and dividing it by the Interceptions Behavior Rate (rate of interception celeration).

Placed on a ratio chart, this value represents the rate of overall improvement, and how well the offense was able to increase correct behavior (passing touchdowns), and decreases bad behavior (interceptions).

A positive value (represented here as a %) would indicate that the offense improved overall at throwing touchdowns rather than interceptions per minute of possession time. A negative value indicates that overall there was a regression. 

1. Chiefs Passing Offense Becoming More Efficient At Scoring 

When you look at raw totals, it can be easy to set aside efficiency. Coming out of the win over the Ravens in the AFCC, some of the talk was about Mahomes and the offense in the second half. 

Mahomes did not throw a touchdown in the second half. There was concern that Mahomes and the Chiefs stalled. In some way they did. But one area of growth for Mahomes has been his ability to adjust to the game flow and take what’s being given. His defense was dominating, and he had a two score lead. 

You know what else he didn’t do?

Throw an interception. In fact, he has yet to throw an interception in the playoffs. He hasn’t thrown an interception in his last four games. This is by far his best stretch of the season. It is the only time all year he has consecutive games, of any number, not throwing at least one interception, throwing five touchdowns in that span. 

2.  Chiefs Passing Offense Becoming More Stable

Heading into the bye week, Mahomes and the passing offense had bounce rates of x3.6 and x3.7 in their Passing Touchdown Behavior Rate, and Interception Behavior Rate respectively. 

 After the bye week, not only did they see their performance dramatically improve, as touchdowns per minute increased by 8% and interceptions per minute decreased by 32.9%, but it also stabilized and became a consistent improvement, that could be predicted. 

After the bye week, they became more stable by 27.6% in passing touchdowns per minute, and 24.3% more stable in interceptions per minute. 

Performance improvement, combined with stable performances, is a good indicator of being internally strong and having goof chemistry. 

3. Chiefs With Good Momentum

All of this goes to the strength of the Chiefs momentum coming out of the bye week. Week to week they getting 20% better at throwing touchdowns vs. interceptions. 

When you combine that with an overall 20+% improvement in consistency in both areas, the strength of their momentum is growing. This means it will take a disruption of significant magnitude to bring an end to that momentum. 

Are the 49ers that disruptor? The 49ers defense has been getting 12.3% worse week to week at forcing interceptions compared to allowing passing touchdowns. Over the course of the full season they have been forcing 9% less interceptions per minute, compared to allowing 4% more passing touchdowns week to week. 

Applied NFL Analytics: Purdy, 49ers Offense On Path Of Convergence

1. Touchdowns and Interceptions Set To Overlap

One of the really interesting nuggets from looking at Purdy’s charts is that since the 49ers bye week, the average of touchdowns per minute he throws has improved by 35%, and the average number of interceptions thrown per minute has decreased by 2% week to week. 

While the increased averages certainly helped improve the index score (by 78%), it was still a negative score, showing a 48.5% deterioration in the 49ers offense’s passing touchdown behavior relative to their interception behavior. 

It’s a good reminder that averages are not a key indicator when predicting behavior. Trends are, or momentum. Purdy’s touchdown throwing behavior has decreased week to week by 39%. His interception throwing behavior has increased 18% week to week. 

This sets those two trends on a post-bye week collision course set to overlap on Super Sunday where he is projected to throw 0.03 touchdowns and 0.03 interceptions. Against the Lions, these rate converged for the first time all season When Purdy threw one of each. Now, Interceptions are set to outpace touchdowns. 

2.  Purdy, 49ers Lack Stability

This isn’t necessarily a bad thing. The highs have been really high. They threw 3+ touchdowns in a game five times. But, the lows have been really low, throwing 1 or less touchdowns in nine games, with seven of them including a net 0 or net negative touchdown to interception ratio. 

That explains why after the bye week, Purdy has bounce rates over x4 in both touchdowns per minute, and interceptions per minute. Those are increases in instability of 29% and 59% respectively. 

The 49ers are clearly hoping to be at the top of their bounce envelopes against the Chiefs.    

3.  Purdy Improved More Than Mahomes

Purdy saw a larger improvement following his bye week than Mahomes did following his, 78% to 62%.

However, Mahomes and the Chiefs offense still performed better, with stronger momentum trends heading into the game. The Chiefs passing offense is in a state of week to week improvement, while Purdy and the 49ers are still in a regression, though that regression has slowed down.  

The 49ers are clearly hoping to be at the top of their bounce envelopes against the Chiefs.  The Chiefs are seeing 6% improvement in giving up touchdowns per minute this season, but that is paired with a 6% regression in securing interceptions week to week.

They have seen no improvement or regression this season in forcing interceptions compared to allowing touchdowns, with an index score of 0%.