The National Football League is the most popular professional sports league in the United States and has a strong grip on American culture. Due to its immense popularity, many statistics and other various pieces of data have been meticulously collected since its inception. Said data has gotten more and more detailed over the years as technology and fan interest have both improved. Simultaneously, the game of football itself has, at the highest level, changed immensely over a very short period of time. This is best reflected in the alterations in league wide offensive success, also known as the scoring environment. The scoring environment of a league is best defined as the ease at which an average offense can score points. The changes seen in the NFL are often controversial amongst fans. Older fans will lament that their favorite players of yore had to play against tougher defenses, while newer fans will cite misleading raw statistics that favor modern players due to the nature of today’s game. Attempts to quantify the environmental changes in the league are often ignored by the vast majority of fans, but it is something that fascinates me and should fascinate you as well.
In order to examine these alterations, I utilized a package in the coding language R titled “nflfastR” in order to quickly scrape play by play data for the NFL. The function “load_pbp” in the package automatically scrapes yearly play by play data from the NFL verse data repository. The data contains an observation for every single play recorded in the NFL since 1999. It contains 373 variables for each play, giving me an immense amount of detail if need be. The data was already in tidy format. However, it was not necessarily in the format I needed in order to examine certain things. I performed various transformations on said data, grouping by different variables depending on what I wanted to look at.
In football, the goal of the team in possession of the ball is to accumulate yards as they advance towards the end zone. If the team reaches the end zone, they are awarded six points, with point after attempt that could potentially (and very likely) make it seven. If a team is unable to score a touchdown within the amount of tries allotted, they can either kick a field goal to earn three points, or if the kick is too long, they can punt the ball to the other team. This simple set of rules have been played with by coaches doing all they can to gain a competitive advantage. Over the years, NFL teams have gotten smarter and more effective in ways they can move the ball in an attempt to score points. This is reflected in the significant increase in league wide scoring since 1999.
Teams as a whole have been scoring more points as time has passed, with the exception of the ongoing 2022 season, a season in which offenses have been mysteriously anemic. There are a few explanations, including a rule change allowing defenders to make more contact with offensive players, and stronger defensive strategies. Still, overall, there is a significant upward trend. The next thing I looked at is whether or not this trend is a league-wide phenomenon, or if it is driven by a change in behavior by a certain class of teams.
This graphic demonstrates a quantile time series regression meant to answer this question. Each data point is a single team in a single season. Based on the percentiles used, it looks like there has been a consistent league wide increase in scoring. The best and worst offenses are both improving at similar rates, indicating an environment change that equally impacts all types of teams. The next thing to consider is how certain offensive strategies are impacting the game.
The graphic above visualizes the league average efficacy of pass and run plays. A pass play is defined as a play in which an offensive player, usually the quarterback, drops back with the intention of throwing a forward pass. These include sacks, plays in which the passer is unable to actually throw a forward pass because a defender tackled them for a loss of yards. These are still considered pass plays, as the team had the intention of executing a forward pass. Rush plays are plays intended to gain yards without throwing a forward pass. They can be handoffs, pitches, or designed quarterback runs. If a quarterback runs on a designed pass play, it is not considered a rush play. As time has gone on, teams have started running the ball less frequently in favor of putting the ball in the air. This is a fairly intuitive trend to expect, as pass plays average considerably more yards. Football is a complicated sport, and there are nuances to the play types that prevent teams from simply throwing the ball every time, but the general tendency as teams gain in information is to throw the ball more. Despite an increase in throwing volume, throwing efficacy has not gone down. This could be due to changes in offensive strategies, rule changes allowing offensive players to get away with more, and other important factors. On the flip side, as teams run the ball less, they are experiencing more success in the run game. An increase in average yardage on both run and pass plays is a clear potential cause of this league wide increase in scoring. However, as seen in the graphic below, league pass rates have plateaued in recent years.
Similar to league scoring, all kinds of teams have experienced substantial improvements in both their rushing and passing success. The worst, average, and best offenses have all tended to improve over time both on the ground and through the air. This further supports the relationship between the increase in yards per play and the increase in points scored.
The increase in rushing yards per play can be mostly attributed to the fact that teams are running the ball less frequently, per the law of diminishing marginal utility. However, if this is the case, then how is passing becoming more effective?
The chart above shots the average depth of target and the average yards after catch. Depth of target is a self evident term that measures how far down the field a receiver is when the quarterback targets him. Yards after the catch is also a self evident term, as it measures the average yards a receiver gains after catching a pass. This data only goes back to 2006, when tracking data became more sophisticated, but it still shows a clear trend. Teams are tending to throw fewer deep passes, and yards after catch has stagnated. If teams are throwing the ball shorter, but not gaining any more yards after the catch, then how are they gaining more yards overall? The key difference is the significant increase in completion percentage, the rate at which a forward pass is caught by a wide receiver. While depth of target has gone down with little increase in yards after catch, quarterbacks are completing considerably more passes and this is allowing for a significant boost to their yards per attempt.
Based on the data presented, the current league tendency with the passing of time is to experience a boost in offensive performance. It is difficult to determine the specific causes of this boost, as there are a massive amount of different factors that influence the game of football. However, I did find two key drivers of the increase in offensive success: higher rates of passing, and higher rates of completed short passes. The higher rate of passing allows for more efficient rushing, while opting for the more effective play type more often. The higher rate of completed short passes helps keep the average yards per attempt high, allowing teams to move the ball more. There is a lot more nuance that can be examined further, but these are seemingly the two biggest factors driving this offensive boom in today’s league.
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