NFL Injury Trends – What The Data Reveals

2017 felt like a particularly brutal year for NFL injuries. Safety concerns have consumed much of the media coverage associated with the NFL. The dangers associated with football are unquestionable but have injuries become more frequent or more severe over time or is it simply that the coverage of these injuries increased?

This article takes an in-depth look at injury data from the last 5 years and focuses more closely on recent injury data in an attempt to get a grip on recent NFL injury trends. Additionally, this article explores the impact of injuries to specific players and how they help to determine a team’s ability to win in the NFL.

NFL Injury Trends – What The Data Reveals

Aaron Rodgers, Deshaun Watson, Carson Wentz and Andrew Luck are just a few of the key quarterbacks that spent the final weeks of the NFL season on injured reserve. Season-ending injuries to stars J.J. Watt, Odell Beckham Jr., Eric Berry, Richard Sherman and Ryan Shazier only added to the feeling that this season was a particularly injury-riddled year for the countries’ most popular league.

While the NFL has yet to release its 2017 injury data, and Football Outsiders has yet to publish their yearly injury report, a look at spotrac.com injury reserve data does reveal an uptick this year in serious injuries.

In 2017, 550 players spent time on injured reserve. This is compared to 496 and 469 in 2016 and 2015 respectively. A more in-depth look at the past few years of injury data reveals some interesting and potentially counter-intuitive conclusions with respect to injury trends, particularly given the recent media attention.

Following the 2016 season, the NFL released the following tables showing injury trends from the period of 2012 – 2016 by injury type.

Even a cursory look at the tables reveals that no distinctive relationship exists between year and injury rate. If anything, the most obvious conclusion is that there has been little to no change over the course of this 5-year period in any of the three injury categories.

One reasonable argument the NFL may make for the stagnation in injury rates following increased attention to player safety and a change in some of the injury protocols would be an increase in injury reporting, specifically related to concussions.

Dr. John York, co-chairman of the San Francisco 49ers echoed this argument in the New York Times, explaining “We’ve seen an increased number of self-reported concussions this year….. I would also say that they have an effect that may cause an increase in the number of concussions that we identify.”

Nevertheless, increased reporting is less likely to have occurred with MCL and ACL tears, and similarly to concussions, there was no increase in injury frequency with respect to these two types of injuries over the 5-year span.While trends in injury frequency and severity are important, it is equally important to understand the impact of injuries on a team’s ability to win.

If a reserve player is injured, his impact on the teams’ ability to win games is far less important than if a star were to be injured. In 2008, Football Outsiders created an injury metric that attempted to quantify not only the frequency of injuries but also the impact of injuries. The statistic they came up with was originally named “Historically Adjusted Games Lost” (HGL) and is now more commonly referred to as AGL.

In 2009, Bill Barnwell, then of Football Outsiders, wrote an article in The New York Times describing the rationale for the AGL statistic, saying:

“making minor observations about a player or team is easy enough, but broader statements about team health require years of data and a metric that neatly encapsulates the information. Football Outsiders has developed several metrics for analyzing injuries; at the moment, the most powerful one is referred to as H.G.L., or History-Adjusted Games Lost.”

The AGL metric builds upon eight seasons of NFL injury data. The data that was used to create the metric was injury data from 2001 to 2008. Each game missed by a player was assigned a numerical value of “injury cost” based on a set of 8 variables. These variables include the player’s role on the team (i.e.: reserve vs starter), previous Pro Bowl appearances, and “the historical effect of injuries sustained by a player of a similar caliber”.

The total number of injuries was found in each group of players deemed to be of a similar caliber. Point values were then assigned to each group of players and were weighted to form the most accurate relationship between the statistic and winning. Each game lost to a player was then assigned a point value. The values ranged from .25 to 1.75 as data revealed that injuries to Pro Bowl Players at a given position were approximately seven times more important to a teams ability to win than injuries to a reserve player at the same position.

Over the years, the analysis of the AGL statistics has revealed some interesting conclusions. Injuries, as measured by AGL, have a huge impact on team success. In 2008, the first year the statistic was calculated, 7 of the 10 healthiest teams made the playoffs.

Barnwell writes “the formula suggests that 26 percent of a teams’ change in wins from year to year can be attributed to the change in its rate of injury.”

Additionally, football outsiders found that injury rates by team are not consistent year to year. That is to say, if a team was particularly hit by injuries in a given year, they are no more likely to be hit by injuries in the following year.

AGL also revealed that injuries at certain positions are far more important than injuries at other positions. For example, injuries at the running back position are of very little significance. Teams who experienced injuries to their starting running backs suffered little loss to the results in their running games in the following weeks.

So what does all this information tell us about NFL injury trends?

While there seems to be no significant trend in the NFL injury rate in recent times, 2017 was a particularly bad year for serious injuries according to the injured reserve statistics. Furthermore, although the football outsiders have yet to release there 2017 injury data report, one would expect a significant increase in the average AGL by team given both the increased incidence of injury as well as the number of injuries to star players.

While one would hope recent rule changes would have led to fewer injuries, the data suggests that the league is moving sideways at best when it comes to this issue.