When St. Louis Rams quarterback Case Keenum sustained a concussion in a game in Baltimore last month, commentators focused on how he wobbled as he got up and questioned why he was not taken out of the game. Few mentioned that he had slammed his head on the turf.

In the rush to reduce head trauma in sports, doctors, researchers, leagues and equipment makers have looked at everything from improving helmets to teaching safer tackling techniques.

But one little-explored cause of concussions is the fields beneath the feet of the millions of athletes who play football, lacrosse, soccer and other sports.

A new report compiled by the Concussion Legacy Foundation called attention to the link between head injuries and poorly maintained fields, especially the growing number of those made of synthetic turf. The foundation urged groundskeepers, athletic directors and sports associations to treat their fields as seriously as other protective sports equipment.

“We have no national conversation on the technology underneath an athlete’s feet,” the authors wrote in their report, the Role of Synthetic Turf in Concussion. “Helmet technology is an area of great attention and investment, and surfaces deserve the same attention.”

The report, which is based on a more than a dozen academic studies, cites research that shows that 15.5 percent of concussions in high school sports occur when players hit their heads on a playing surface. Another study found that 10 percent of concussions sustained by high school and college football players came after players hit their heads on a field.

In the NFL, about 1 in 7 concussions occurs when a player’s head strikes a synthetic or grass field.

The percentages may appear small, but they amount to thousands of head injuries a year. While far more concussions still occur from helmet-to-helmet hits and other collisions, the authors note that keeping fields from becoming too hard can prevent head injuries.

A vast majority of playing fields nationwide are still natural grass, and they too can become dangerously hard, particularly in cold weather. Harder fields absorb less of a player’s energy when he or she falls, increasing the risk of injury.

Synthetic fields, which are typically made of a mix of sand, rubber pellets and plastic fibers that sit on gravel, pose a different challenge. Costing hundreds of thousands of dollars or more, they have been marketed to schools, cities and teams as a way to reduce maintenance costs and increase usage, though the savings, if any, can vary widely based on how frequently they are used. No seeding, fertilizer or mowing is needed, and the fields can be used in many types of weather, but they must be replaced every decade or so.

The number of synthetic fields has grown to more than 12,000 nationally, and about 1,500 fields were installed this year, according to the Synthetic Turf Council.

With proper upkeep, synthetic fields are considered as safe as natural grass, even though they can be used far more often. But routine maintenance like raking of the rubber pellets and tilling of the sand is required to ensure the field does not get too hard. Rubber pellets must be replaced when they wear away from goal creases and other high-use areas of fields.

Despite the increase in synthetic fields, precise data on how they are maintained is spotty. Experts who maintain fields professionally say many schools and parks departments forgo basic maintenance and do not test their fields to determine whether they have become too hard because they are unaware it is needed or because they want to keep costs down.

“Artificial fields are still sold as maintenance-free — you put it down, you don’t worry about it — but honestly, they’re hardly being maintained at all,” said Dr. John Sorochan, co-director of the Center for Athletic Field Safety at the University of Tennessee. “People put in the fields because they don’t want to budget for it once they’ve got it.”

Few athletic directors and groundskeepers are willing to admit that they do not properly care for their fields because it may open them up to a lawsuit or void their warranty, which is typically eight years, according to industry experts. But Gary Hover, the former director of parks and facilities in California who now owns a turf maintenance company, said he had seen fields that were rarely maintained.

“They didn’t know what they didn’t know,” he said of the groundskeepers. “Artificial fields wear out.”

Synthetic turf makers say their products are safe when used correctly and point to academic research that shows that injury rates of synthetic fields and natural grass are roughly similar, and nearly indistinguishable for concussions.

“Statistically, there’s no difference between the two when it comes to concussions,” said Michael C. Meyers, an associate professor in the Department of Sport Science and Physical Education at Idaho State University. “When you break it down player to player, there is not a field turf problem.”

Still, concussions and other injuries are always a concern, so turf companies have been doing more to teach their customers how to keep their fields from getting hard. Darren Gill, the vice president for marketing at Field Turf, the industry leader, said his company taught customers to brush, aerate, rake and sweep their fields. Customers are told to measure the rubber infill in the field and add more when it wears away.

“The clients need to do their maintenance, and some do and some don’t,” Gill said. “We believe if our protocols are followed properly, the field will be in good condition. The good news is the maintenance is not arduous, but there is still work to do.”

The Synthetic Turf Council publishes voluntary guidelines for maintaining fields and for helping manufacturers and installers teach their customers the best ways to preserve fields, said Al Garver, the president of the council.

Keeping synthetic fields in top shape, though, can take a lot of work, even with ample resources. At M&T Bank Stadium, where the Baltimore Ravens play, groundskeepers drive a LitterKat synthetic turf sweeper, a machine that costs about $8,000, across the field for four hours two or three times a week to ensure the rubber is cleaned and evenly distributed. The team uses a Clegg hammer, a device that costs about $3,000, to confirm that the field’s hardness is below the NFL’s limit.

If it is not, workers may spread more rubber pellets on the field using a top dresser machine. The team keeps one-ton bags of pellets in stock for the task. Don Follett, the head groundskeeper for the Ravens, also said the league required that the field be repainted every four games because the paint can become hard.

Even so, the top 12 fields in the league were grass, according to a poll of NFL players by Sports Illustrated.

In Kansas City, Clark Hunt, the owner of the Chiefs, said synthetic turf might be more efficient, but he keeps natural grass in Arrowhead Stadium because his players tell him they prefer it.

A host of companies are looking for ways to improve synthetic turf fields, including by adding high-tech cushioning below the fields to dampen the impact when players fall. One company, Viconic Sporting, has received $1.25 million from the NFL, GE and Under Armour to help develop its padding technology now used in automobiles under turf fields when they are installed.

The pads add about 10 percent to the cost of installing a field, which can exceed $1 million. But with thousands of synthetic turf fields installed, schools, municipalities and teams need to maintain them properly to reduce the risk of injuries, experts said.

“Even a Mercedes needs oil in the car,” said Joe DiGeronimo, whose company, DMA Sports Design, tests synthetic fields, including at one time those in NFL stadiums. Some manufacturers “forget to tell the buyers, if you do a little maintenance, the fields will do better.”

© 2015 The New York Times Company