Credit: Illustration by Slug Signorino

A rugby player friend of mine says one reason for the serious injuries in American football is pads and helmets. He says players can hit harder because of protective equipment and do so knowing they will suffer less injury than those on the receiving end. Also, he claims that if players went back to one-platoon football, meaning they played both offense and defense, the size of the players on offense and defense would be smaller and more equal and there would be less chance of a big, fast linebacker laying flat a receiver or quarterback. Any truth to either of these lines of thought, or is it just rugby snobbery? —Sam Johnson

It’s partly rugby snobbery, but never mind. Is it true? Probably yes.

The concept here is called risk homeostasis or risk compensation. It holds that everyone engaged in a dangerous activity has a personal risk-vs.-reward level they’ll stick to no matter what—if you force someone playing a contact sport to wear protective equipment, they’ll take bigger risks to bring the danger back to the level they’re comfortable with.

Does that sound self-destructive? If only. When risky behavior increases, others may bear the brunt. A watershed 1975 study of automobile safety measures theorized that motorists increased their driving “intensity” if they felt safer behind the wheel, leading to fewer driver and passenger deaths but more dead pedestrians.

Applying this theory to football, one might suppose that as players switched from leather helmets to today’s elaborate headgear, they’d hit harder and generally play more recklessly. In fact that seems to be what happened.

When hard plastic football helmets became popular after World War II, tackling methods shifted, so that by the early ’60s players had gone from tackling shoulder first to head first. Possibly as a result, tackling injuries in the years from 1955 through 1964 rose significantly compared to a decade earlier. This eventually led to rule changes, notably a ban on “spearing” (hits delivered via a lowered head), and better standards for helmets.

To be clear, helmets do work—up to a point. Experiments have shown, for example, that a helmet reduces the impact of heading a soccer ball traveling at 35 MPH from 19 g to 8 g. But protecting against obvious dangers often just makes the problems more insidious. While helmets reduce skull fractures and deaths, they also encourage players to endure frequent concussions that over a career add up to brain damage.

Risk compensation isn’t limited to football. A study of little leaguers found kids using soft rather than standard baseballs suffered more injuries, probably due to taking bigger fielding risks and being less afraid of wild pitches. Researchers also found that rugby players who wore helmets tackled harder than those without, and the use of quick-release bindings and helmets by skiers and snowboarders may have led to more risk-taking and associated casualties.

Risk compensation may not apply to all sports, though. Studies have found hockey players wearing only upper-face protection get injured more than those wearing full face masks and are more likely to engage in illegal behavior. Helmet-wearing bicyclists not only suffer fewer serious injuries but also use hand signals more and obey the rules of the road.

On closer examination, though, those two cases may not be exceptions after all. Bike helmets are generally optional, and anyone who wears protective headgear without being compelled to is by definition a cautious sort. Likewise, you have to wonder if differences among hockey players can be attributed to more aggressive types who pick headgear that offers less protection.

A concept related to risk compensation is moral hazard, where people do dangerous things because they won’t suffer the consequences. One much-studied question is why American League batters have gotten hit by pitches 15 percent more often than their National League counterparts since imposition of the designated hitter rule. For many, the explanation is obvious: since AL pitchers don’t bat, a beanball thrower doesn’t risk retaliation. But some researchers say an equally important factor is that DHs are much better hitters than the pitchers they replace and thus likelier targets for brushbacks and beanings.

Finally, would going back to one-platoon football would make the game safer? There’s virtually no data. On the one hand it seems obvious that if the same squad had to play both ways, no team could afford 300-pound linemen. Then again, linebacker Lawrence Taylor, whose brutal quarterback sacks famously gave rise to the 300-pound blind-side offensive tackle, was a relative lightweight at 240 pounds. So I’m not convinced a no-sub rule would give us a kinder, gentler game.

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