When the umpire shouts “play ball,” chances are it’s a bunch of kids being called to action. Baseball belongs predominantly to the world’s youth, and their safety on the field is a constant concern of officials at Little League Baseball Inc., the world’s largest organized youth-sports program.

When Little League administrators began to consider whether they should encourage the use of face guards and soft-core, reduced-impact “safety balls” to mitigate injuries, they wanted data to back up the idea. “Otherwise,” says Dan Kirby, an official at Little League headquarters in Williamsport, Pennsylvania, “it’s just people making assumptions.”

Enter Carolina’s Injury Prevention Research Center, where affiliated scientists Stephen Marshall and Fred Mueller, with a team of graduate students, conducted the first “epidemiologic” study ever done to test reduced-impact balls and face guards for risk mitigation. In a three-year effort, the researchers contacted all 5,000-plus U.S. leagues, by mail and later by telephone, to identify where the safety devices are used and where they are not. Marshall then overlaid that survey data onto a national database of compensated insurance claims maintained by Little League. Findings, gleaned from an analysis of more than 6.7 million “player-seasons,” show a 23 percent reduced risk of ball-related injury associated with safety balls, and a 35 percent reduced risk of facial injury among players using face guards.

But the study also indicates that safety balls and face guards do not prevent all injuries. Benefits are greatest for younger players, who cannot as skillfully avoid ball impacts as their more experienced counterparts. But thanks to UNC-Chapel Hill researchers, persons urging adoption of safety balls and face guards in their local leagues now have useful ammunition for making their argument.