Theory of Impact – How to Quantify Impact in American Football

Theory of Impact – How to Quantify Impact in American Football

By: Adam Carter | adamkinsleycarter@gmail.com | Twitter: @adamcarterfb

Described is a statistic used to evaluate talent in American football. An Impact is a stat that measures the number of times a player is in position to make a play on the ball. Impact% is the percentage of times a player gets in position to make a play on the ball divided by their total snaps played. Its practical purpose is to serve as an evaluation system for defensive and special teams players, providing a distinct competitive advantage to scouting departments and coaching staffs. This innovative concept of measuring a player’s ability to position themselves for a play on the ball can also be applied to evaluate players in other sports, such as soccer, rugby, basketball, and lacrosse. 

Impact% is meant to be a process stat that gives you a holistic understanding of how impactful a player is. It rewards a player for getting himself in position to make a play on the ball, even if the result of the play doesn’t go his way. Impact% gives you an accurate read of how a player is performing because it considers his process and results-based actions on the field. For the most part, a player who isn’t consistently around the ball isn’t impacting the game. While there are things you can do to impact the game away from the ball, a player’s impact is only felt if he is around it. Measuring a player getting himself in position to make a play on the ball is rooted in the idea that there are different ways to measure football production beyond box score stats. Instead of solely looking at a player’s tackles, interceptions, sacks, or pressures, Impact% measures actions like tight coverage when targeted or redirecting the ball carrier at the line of scrimmage as measures of productivity. This gives you a list of players who give your team hidden advantages on game days. When charting during the 2023 season, one player on the team had only seven tackles but got himself in position to make a play on the ball 28 times. This is a perfect example of how the box score and traditional results-based advanced stats may not accurately capture football players’ proper production and value. Despite a player’s contributions not showing up in the box score, they may still be getting themselves in the correct position to impact the game, even if the result doesn’t go their way. This is the indicator of a player with a good process. 

A loaf can be measured in multiple different ways. The number of times you get yourself in position to make a play on the ball and fail to do so. When you’re in close enough position to make a play on the ball and fail to do so. When a player is out of position, the ball comes his way, which allows the offense to gain extra yards. An example is a linebacker blowing his run fit and letting the ball carrier run through his gap into the second level. Had the linebacker been in position, he would’ve at least been able to generate a play on the ball with the opportunity to convert the play. Instead, he only gets credit for a loaf because he couldn’t contest the play. This is also an example of how a player can generate a loaf without getting credit for a play on the ball. Another example of this type of grading is when a cornerback allows a catch on a target where he isn’t in the picture. Even though he wasn’t around the ball, had he covered the receiver better, he would’ve been, which would’ve counted as a potential opportunity to make a play on the ball. This goes down as a loaf and lowers your conversion rate because, ultimately, this was an opportunity to convert a play on the ball that was missed. The instances in which a defensive player wouldn’t be penalized for allowing a catch are on screens, quick passes, or catches that go for minimal or no gain.

An example of a neutrally graded play is a cornerback in tight downfield coverage who allows a catch. Even though the corner allowed the ball to be caught, he was still in tight enough coverage to impact the play and make it a difficult catch for the receiver. He would get credit for being in position to make a play on the ball, as you are anytime you’re in tight coverage, but would also get credit for a loaf because the pass was caught. On most grading sites, this would be a negatively graded play because the corner allowed an explosive catch. Depending on the degree of difficulty on the catch, there’s a chance that 7,8,9 times out of 10, that pass doesn’t get completed. This is an example of how defensive backs can sometimes be victims of contested catch variance when it comes to grading. Additionally, this indirectly measures how good a corner is at limiting separation, even if they allow catches. 

Loafs are critical defensive errors because they allow the offense to gain extra yards and stress the defense more. Players who loaf a lot tend to play out of control and are often out of position. They usually play out of the structure of the defense or can’t convert the opportunity when they get an on-ball attempt. The best way to avoid loafing is to play within the structure of the defense. Playing within the defense’s structure mostly means understanding your assignment at the highest level, ensuring you’ll always be in position when the ball comes your way. This way, you will avoid being penalized for any out-of-position loafs. This emphasizes the basic point that good football players loaf less than bad ones. 

For any scout or general manager evaluating a player, somebody with a high Impact% and low Loaf% is a player who is frequently in the right spot, consistently involved within the flow of the game, and somebody you can trust when the ball comes their way. A player with a high Impact% and Loaf% can still be worthy of investment if you can teach them to loaf less. These are good examples of players who you can coach the mistakes out of. A player with a low Impact% is usually somebody who is not very good. A cornerback who consistently gets beat would have a low Impact% because they aren’t giving themself a chance to record a play on the ball. A defensive lineman who struggles to win reps would also have a low Impact% because, similarly, they aren’t giving themself a chance to record production. 

Conversion rate is your total impacts – totals loafs divided by total impacts. This stat tells you how well you do at converting the opportunities presented to you.  From the charting I’ve done, you notice that the best players on our team convert their opportunities at the highest rate in addition to having the highest Impact% in their room. Conversion rate is the football equivalent of batting average or shooting percentage. A player with a high conversion rate but a low Impact% may be an example of somebody the defense should try to create more opportunities for as he has a high probability to convert them. This is an essential stat for defensive backs as they naturally don’t see as many opportunities, so they must convert the ones presented. A player with a low conversion rate but a high Impact% is an example of a volume producer who is taking away opportunities from other players. They can get themself to the ball but can’t convert the opportunity. This would be like a volume scorer who averages close to 30 ppg but barely shoots 40% from the field in basketball. In baseball, it would be a home run or bust type hitter who hits 40 homers a season but only hits .210.

Like a player with a high loaf%, this is an example of a player who could become elite if he can get the negative plays in check. In basketball, converting above 45% of your shot attempts is usually the sign of an average shooter. In baseball, getting a hit 25% of the time is the sign of an average hitter. Converting above 80% of your on-ball opportunities is usually where you want to be in football. 

DER, I’ve concluded, is the best measure of on-field productivity. DER is the weekly cumulative sum of your total impacts divided by your total loafs. A player with three impacts and one loaf would have a DER of 3. A player with seven impacts and two loafs would have a DER of 3.5 for that game. When you add them up, that player would have a DER of 6.5 after those two games. The reason why it’s calculated this way is because I don’t want what you do in another game or setting to take away from what you did the previous day. DER is meant to be your efficiency/production score for that day. It’s not supposed to be influenced by anything other than what you did that day. DER is the stat that consistently props up your top performers. It’s meant to be your ratio of positive to negative plays. A player with an 8:1 ratio of positive to negative plays is probably somebody you’d want on the field. When charting for the University of San Diego football during the 2023 season, all our best players were at the top of this statistic. When comparing the DER scores to Pro Football Focus grades, I found that the two had a robust correlation. The five highest defensive players by PFF grade were also the five highest by DER in 2023. In total, 7 of the 10 best DER scores were also included in PFFs 10 highest graded players on the defense. 

Range% is your total impacts – total loafs divided by total snaps. Whereas Impact% considers loafs where you were in position and didn’t make the play, Range% excludes all loafs from the equation. This gives you a player on-field success percentage—the percentage of plays he is successfully involved in. The reason I call it range is because players with lots of on-field range and versatility are the ones who do best in this. Players who can affect the game in multiple different ways make themselves a threat on every play. Thus, they will score higher in this statistic. 

Impact% is a statistic that can be of great use to coaches. There are a few ways that even an offensive coordinator can use Impact% to his advantage when game planning. Figuring out where and when a defense loafs would be vital in knowing how to put stress on a defense. While charting, I discovered two common themes when a defense allows a big play or a touchdown. The first is when there were a lot of players in position to make a play on the ball, but many of them loafed, allowing the ball carrier to continue their momentum down the field. This happens on explosive run plays where a linebacker loafs, leaving the secondary to bring down a running back moving at full speed in the open field. The other is when there’s nobody in position to make a play on the ball, meaning nobody has the opportunity to finish the play or affect the ball. You see this happen frequently on deep passes where the quarterback throws the ball over the top of the defense so nobody can make a play on it, and the receiver can outrun the secondary into the endzone. This also happens when the offense executes their blocks perfectly on any run or screen call. When self-scouting your run game, you can see the number of defenders in position to make a play on the ball at the line of scrimmage for each call. This would give you keen insight into which plays you block the best. If there’s a specific route where a corner has a high Impact%, you’d probably want the quarterback to know not to throw the ball in those circumstances. Detailed knowledge like this could give an offensive coordinator a hidden advantage on game day.

For a defensive coordinator, when you break down Impact%, DER, and loaf% on specific play calls, you can compare them by position and see which players are best at getting to their spot and converting the opportunity. If a defensive coordinator has called the same blitz with multiple players at the same position, you can see which one was more impactful when asked to do the same thing. If you’ve performed a specific stunt with your defensive lineman, you can see which ones are the most impactful when asked to perform the same task. You can also know when a player is struggling with a specific assignment or technique on a play with loaf% and figure out if there’s somebody else at that position who can perform it more efficiently. This is an intelligent way to identify who your best 11 are on every play call. Looking at where a player is loafing could give you insight into his areas of deficiencies on the field.  It also gives you an easy solution for where the player should focus if he wants to improve. This is another way Impact% can be a potent teaching weapon for any coach. This allows you to go in and look at the root of a player’s mistakes. Going in and correcting a player’s on-field mistakes could allow you to change the course of someone’s career quickly. Overall, a defensive coordinator should want players who get themselves in positions to make plays on the ball and avoid loafs. 

The Impact% grading system can also be used in special teams. Special teams are an underexplored avenue of the football statistics world. Impact% is the perfect stat for a special teams coach to evaluate his position group. This would be a new-age way to assess all other players in a kickoff or punt that don’t include the kicker, punter, long snapper, or return-man. Finding a way to evaluate most players on the field in these situations would be a great way to give your special teams unit an edge every week. Measuring how consistently somebody can win those matchups would be important in determining who should be on the field. 

I created Impact% because tackle statistics in football can be very misleading, especially when a player has a high number of assisted tackles. Tackles are people’s primary stat to gauge how impactful or productive a player is. Looking at the times when a player was in position to make a play on the ball is more valuable than a tackle. Often, tackle statistics credit players who come in late, which is unfair to the defender who was on time and in the right spot, only to be rewarded with 50% of that tackle. It hurts the defender who brought the ball carrier down to the ground and unfairly rewarded a player who wasn’t involved with the play in any way. Players can cheat their way into high tackle numbers by coming in late and jumping on the defender as he’s falling to the ground. This is why, when charting for Impact%, any action counted towards being in position to make a play on the ball must be completed before the ball carrier is in the process of falling to the ground. Any player that comes in after that thinking they’ve contributed to the play will not be counted. It’s the difference in verbiage between a “tackle” and “play on the ball.” Even when it might be a bang-bang play between two players going for the ball, you still have to ask yourself, “Who made this play?” 

This article describes a patented football grading system that brings a new way of thinking to scouting and grading film. Impact% is a production-based grading system that measures players who get themselves in position to make a play on the ball. It yields highly accurate results and finds undervalued players on your defense/special teams units. It can also help your offensive coaching staff have significant scouting knowledge of the opponent. This knowledge level would be very valuable for high school programs and small college programs. It’s currently in use at a division one program and has been for the past two years. Adam Carter is now focused on turning Impact% into a business for high school and college coaches. If you want free Impact% data on your players, please email adamkinsleycarter@gmail.com.