As new research emerges, the connection between football and brain injuries seems more substantial – and severe – than ever before. One 2017 study of the brains of deceased NFL players found chronic traumatic encephalopathy in 99 percent of them. Worse still, scientists now believe repeated CTE is caused by any repeated impact, rather than by concussions alone. As the NFL attempts to respond to this rising tide of warnings, the league’s future seems uncertain. Can professional football still flourish as America confronts proof that its favorite sport may be dangerous?
Into this broader narrative, however, few fans and critics understand the complex details of the football safety debate. In this project, we’ll take a deeper look at the perils and precautions of the modern game and analyze some of the more jarring NFL hits in recent memory. To do that, we’ve employed modeling from the field of physics to estimate the impacts of brutal tackles on the brain. From the historical trends in headgear to the most wince-worthy hits of the last few seasons, we’ll show you a side of this issue you’ve never seen before. Keep reading to learn the true hazards of the NFL’s most brutal hits.
Progress on Protection
While it’s hard to imagine bare heads facing off at the line of scrimmage, protective headgear was merely optional during football’s infancy. Started in 1879 as an adapted version of rugby, the game relied on leather helmets for its first six decades – if players bothered with them at all. That tradition began to change as plastic became more widely available post-World War II. In 1939, John Riddell created the first plastic helmet to prevent athletes from cracking their skulls. As the 1940s continued, the NFL adopted new safety technology, adding chin straps, team colors, and emblems (as well as a mandatory helmet policy).
If Riddell’s innovation spared skulls from splitting, however, it did not completely preserve their contents. The addition of face masks in the second half of the 20th century – while important – also did not directly address risks of injury to the brain. As public concern about such injuries multiplied, 2015 ushered in helmets with updated contours and shock-detecting chin straps. 2017 saw a few players experiment with new brain-conscious helmets as well, although critics caution they are far from a panacea for recurring head impacts.
Regulating the Risks
Responding to concerns from the medical community and general public, the NFL has also recently reconsidered many of its rules to mitigate massive hits. Following these rulebook revisions, the number of concussions sustained around the league has fluctuated. Incremental progress seemed to take place beginning in 2012. Thatseason included an important expansion of the “defenseless player rule” to include defensive players being blocked. NFL players also saw a significant decline in concussions following another safety-minded rule change in 2013, when hitting with the crown of the helmet was outlawed for both runners and tacklers. The trend continued through 2014 when just 162 concussions occurred during pre-season, regular season and postseason games, in part thanks to a rule that expanded on “clipping,” a penalty where a player is blocked in the back . But in 2015 and 2016, in-game concussion totals surpassed 200 once again, dashing hopes of enduring change.
Most recently the league’s Competition Committee considered expanding the rule to ban contact initiated with the “hairline” area of the helmet, rather than just the very top.
In a direct comparison with common G-force examples, it is clear that these players’ bodies have experienced shocks that very few on this planet ever have. G-force is a measurement of the force of gravity on a person’s body relating to its acceleration. Most ordinary people will never experience even G-forces of over 5.0 which can be found on thrilling roller coasters, and even those in the military or space programs will likely only reach a few Gs more than that. In comparison, Matt Moore – whose situation is explained in more detail below – experienced an estimated G-force of a staggering 87.4g.
Halfway down the list is a hit to Rob “Gronk” Gronkowski, where he experienced a G-force reaching 46.7, which is equivalent to “The Fastest Man on Earth” John Stapp’s “Sonic Wing” rocket sled ride and about 6.5 times as much as Apollo 16 on reentry.
Some of the more troubling incidents have been detailed below.
Punishing the Passer
In our first in-depth analysis of some of the NFL’s most gruesome hits in recent history, Miami Dolphins quarterback Matt Moore quite literally took one on the chin from Steelers Bud Dupree in 2017. Fans remembered the hit for its brutality, but also for Moore’s apparent persistence: He was back on the field after only one play and missed just one snap for the remainder of the game. When reporters quizzed head coach Adam Gase about sending his player back onto the field so soon after the monstrous collision, he insisted Moore cleared league and team standards.
Our analysis, however, indicates Moore’s brain was subjected to 87.4g of force as a result of Dupree’s impact. If that calculation has your head spinning, imagine how Moore must have felt. The league later determined the Dolphins ignored possible concussion symptoms when they allowed him to retake the field, failing to observe he was bleeding from his mouth after the hit.
The Safety’s Unsafe Play
On many high-speed plays, the tackling player actually gets the raw end of the impact. That was the case for safety Kam Chancellor, whose 2011 tackle on the indomitable Anquan Boldin resulted in two sources of pain: a $20,000 fine and concussion. Boldin seemed surprisingly spry just seconds after the illegal helmet-to-helmet exchange, popping to his feet while Chancellor lay sprawled at the 15-yard line.
The defensive player had good reason to remain down: His hit exerted a G-force of 59.1g. to his brain. Boldin should count himself fortunate, however, as Chancellor’s tackles earned him infamy around the league. This incident seems not to have slowed his appetite for aggression, either: The following year, he pulverized veteran Vernon Davis with an Earth-shattering hit near the end zone, giving the tight end a concussion. Davis later recalled the incident as the hardest hit he took in his career.
Unfortunate or Unacceptable?
When Ryan Shazier knocked Giovani Bernard out cold in a 2016 wild-card game, the play would have been memorable for its violence. But the play is best remembered by Cincinnati Bengals fans for what it lacked: a penalty call. According to the league’s targeting rules at the time, the hit was completely legal, a loophole commentators called “unfortunate” as they replayed the carnage for their viewers. Some experts complained the play indicated how narrowly officials interpreted player protections, claiming Bernard was clearly victimized in a vulnerable moment.
Two months later, the league acknowledged these criticisms and banned hits of this variety. According to our calculations, the hit might have been much worse, however. Because Bernard halted momentarily before Shazier tackled him, his own momentum did not contribute to the impact. As a result, the G-force applied toBernard reached 12.4g. Even in comparison to some larger hits that have been discussed, the effect on his body was still staggering.
The Battered Bronco
When Rodney McLeod collided with receiver Emmanuel Sanders in a November 2014 matchup, both players moved so quickly it was difficult to tell if their helmets had collided – even with the benefit of replays. Nonetheless, the tackle produced a a shock to a defenseless Sanders in the form of 44.8g and 15-yard penalty for a hit above the shoulders
Sanders left the game with a concussion, and an altercation among both the players’ teammates ensued. Neither of these outcomes should be particularly surprising given the sheer intensity of the tackle and vulnerability of its victim. The fact that Sanders was diving for a catch and was totally surprised by the collision only deepened the danger.
Running Back Risks
No NFL running back can afford to shy away from tacklers toward the end of a play, but some yards-after-contact tactics are riskier than others. Running back Devonta Freeman learned the hard way as his Falcons took on the Coltson November 22, 2015. With Clayton Geathers closing in for impact, Freeman seemed to lower his helmet. The resulting collision between the players’ helmets rocked Freeman’s brain to the tune of a G-force reaching 63.5g., according to our calculations.
Freeman staggered off the field, and his injury was later confirmed as a concussion. The incident in Freeman’s rookie season was a rude introduction to the NFL’s physicality, but the player’s history with concussions has since continued. He sustained two concussions during the 2017 season, observing the league’s protocol in each case.
Safety and the State of Play
Our findings suggest significant progress in awareness of brain injuries in professional football, as well as new tactics to address them. New rules eliminating head-to-head collisions and designing new helmets have the potential to reduce the G-force significantly if they create a longer Distance-to-Stop, the distance after which the player’s head comes to a stop after a collision. Model calculations show that this is the critical parameter in determining the G-force. This is similar to a car approaching a red light, in which the driver slams his foot on the brake to come to a stop. The stronger he depresses the brake, the shorter the braking distance will be and the larger the G-forces acting on the passengers. Our model calculations show that under the same conditions like player speed and impact angle, body-body collisions generate a three times lower G-force on the brain than head-head collisions because of a larger Distance-to-Stop. New helmet technology makes use of the same effect. In addition to softer material, more space is added between the skull and the outer layer of the helmet resulting in a larger Distance-to-Stop and therefore lower G-forces on the head.
But make no mistake: The NFL is far from concussion-free and is unlikely to achieve that ideal soon, if at all. Some maintain these injuries are integral to the nature of the game, and that gridiron competition can never truly exclude them. Others insist the risks are too high for the sport to continue. Whatever the fate of the NFL and its players, one thing is certain: Fans and detractors alike will likely be watching closely.
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To present our findings related to the helmets worn by players throughout NFL history, we relied on research gathered by the Smithsonian Magazine. Our discussion of the evolution of rules employed by the league to protect players was informed by numerous sources, all of which are listed on the associated image.
Our calculations related to the force of each tackle involved complex Newtonian physics modeling. Due to the number of variables at work in any on-field collision, however, we cannot claim definitive accuracy for all our results. Accordingly, our findings should be interpreted as purely exploratory, and we hope additional research will further illuminate the subject.
We would like to thank Hauke Kolster, Ph.D., physicist and neuroscientist, for his scientific support of the G-force calculations.
For those interested, information on how our calculations were completed is below:
Using video footage, we calculated the estimated speed of each player involved in the collision (Source: ‘Acceleration-Deceleration Sport-Related Concussion’: The Gravity of It All; Journal of Athletic Training, JT Barth et al., 2001;36(3):253–256).
Calibration of acceleration a to player speed v for Head-Head collisions: a=98 g @ v=9.3 m/s (Source: ‘Concussion in professional football: reconstruction of game impacts and injuries’, Pellman et al., Neurosurgery, 2003, 53(4):799-812.)
DTS (Distance to Stop), one player helmet: 0.0225 m (calibration), one player body: 0.675 m (estimate 3x DTS helmet).
Head-Head collisions, DTS = 0.0225 m + 0.0225 m = 0.045 m
Head-Body collisions: DTS = 0.0225 m + 0.0675 m = 0.09 m
Body-Body collisions: DTS = 0.0675 m + 0.0675 m = 0.135 m
Fair Use Statement
You’re welcome to share our findings and images with your own audience, so long as you do so for non-commercial purposes. If you do use our work, we ask that you attribute us to our efforts by providing a link to this page. After all, not getting credit for our work hurts – although probably not as much as an illegal hit would.