One of the most common complaints about Soldier Field as a football venue has to do with the playing surface. Fans and talking heads complain that Soldier Field’s grass is dangerous to players and is responsible for any number of injuries. To this, the various folks who make high-level decisions for the Bears have normally responded that grass is actually safer. For example, ESPN Chicago quoted George McCaskey back in 2011:

"It's at this point, primarily it's a safety issue. The studies aren't conclusive, but the studies that we have looked at have shown a higher incidence of lower leg injuries among players on artificial turf. And we want to prolong careers. We want our players to be safe. We want our investment in the players to be protected and the state of artificial turf or an infield surface is such now that we think the safest surface for our players is natural grass."

A number of people disagree. Some of them vocally. However, most of those people are not using actual evidence, but rather personal observation. To be clear, George McCaskey is right (at least about this). Most major studies that demonstrate one playing surface has an advantage over another tend to support the idea that grass is a safer playing surface than turf. Moreover, these are not studies from the dark ages of synthetic turf, either, but rather recent examinations of popular and well-regarded synthetics on fields currently.

For example, a major study published in the American Journal of Sports Medicine studied 10 seasons from 2000-2009, looking at 2680 games (or twice as many “team games”, when remembering that each game has two teams). Using some pretty sophisticated analysis and lots of hard work, the people involved in the study looked at lower-body injuries and came to the following conclusion.

“Injury rates for ACL sprains and eversion ankle sprains for NFL games played on FieldTurf were higher than rates for those injuries in games played on grass, and the differences were statistically significant.”

Well, that seems important. So does another study conducted by Dr. Jason Dragoo of Stanford where he found essentially the same thing—that lower body injuries (ACL tears, in his case) went up on artificial turf. In fact, you’ll have a hard time finding a study that says something good about artificial turf unless you encounter the work of one researcher, Michael C Meyers. If you click on the link for his name, you will find that he is an extraordinarily well-credentialed individual who probably understands way more about sports injuries than I ever will.

However, there’s an issue. Meyers has been a consultant for Field Turf USA since 2006, and per his own C.V. he has received more than a million dollars in grant money from Field Turf in support of those studies (as a side note, and perhaps only interesting to me, is that while researching this article I learned that Field Turf is actually headquartered in Montreal). None of this is conclusive evidence of anything wrong, of course, but it is enough of a conflict of interest that it should make anyone skeptical.

Thus, while Meyers’ research clouds the waters enough that ‘studies are inconclusive,’ that level of ambivalence should be taken with a grain of salt. On this, I agree with the editor of the Clinical Journal of Sports Medicine, Dr. James MacDonald, when he refers to the same study:

“One dimension to which I am always particularly sensitive is the funding source for a study. In this case, the research was funded by the product maker itself, FieldTurf. My overall take on this study then is that it is intriguing, but the strength of the findings are not overwhelmingly substantial (i.e. its ‘clinical significance’ is unclear to me), and its chief weakness is that the study was funded by the product maker, something I would always rate a potentially significant limitation.”

So, the worst that can be said about grass is that it is in the same league as synthetic turf in terms of danger, and there’s a high degree of likelihood that it’s safer, at least overall.

Most of these studies focus on lower leg injuries, and that’s because that is the type of injury that can actually be shown in reliable studies to link up with playing surface. There is some burgeoning research on concussions, and a white paper from the Concussion Legacy Foundation began to tackle the subject, but so far results seem to line up with other findings—if there is a difference, it’s a difference that favors grass.

That leads us to Soldier Field, specifically. Because what all of these studies might leave out is the idea that while grass fields in general are safe, maybe Soldier Field is particularly dangerous.

It’s not.

For this conclusion, we do not need to speculate about probabilities. Football Outsiders recently studied every major stadium, and their methodology was compelling. They reduced the impact of a particular team’s training staff and conditioning regimen by looking only to the rate of injury for visiting players. This neat workaround cuts their subject pool in half but it also creates a much more controlled sample to study. Gone are concerns that one particular team might be composed of aging vets with poor training, and so that source of skew is limited. Each field should see a range of different opponents, and mo one team’s limitations should be over-represented.

First, their conclusions aligned with those of most researchers:

“About half of stadiums are natural grass -- 16 of 31 over this period, to be precise -- and they dominate the lower end of injury rates. The most common artificial turf is Field Turf, which covered five stadiums over this period. The upper end of injury rates is dominated by artificial turf stadiums.”

What about Soldier Field? Across the 4-year span that was studied, it had the eighth-lowest (lower leg injury) or ninth-lowest (overall injury) rate for visitor injury in the NFL. This suggests, pretty heavily, that Soldier Field is fine and that whatever combination of decision-makers dictate the continued use of grass actually do know what they are talking about in this case.

The linked Football Outsider articles do explore some alternate explanations, but the fact of the matter is that multiple research articles ranging across medical journals and sports analytics folks come to the same conclusion independently—grass is no more dangerous than synthetic turf, and it’s probably safer most of the time. Additionally, Soldier Field is about in the middle of safety for grass stadiums. That meant it was one of the safer stadiums when it came to avoiding injuries.

Grass didn’t break Quintin Demps’ arm, nor did it uniquely ruin Kyle Long’s ankle. If the Bears really are getting injured more than other teams (and it seems sort of like they are), then at least their home venue is not to blame.