Mike Trout wears a C-flap. Bryce Harper does, too. They’re among 10 players in Tuesday’s MLB All-Star Game who wear attachments to their batting helmets that are designed to protect a batter’s cheek and jaw.

But your Little Leaguer likely can’t wear one — and the reason is a whole other kind of flap.

The National Operating Committee on Standards for Athletic Equipment says add-ons to athletic helmets potentially void manufacturer safety certifications. Amateur baseball governing bodies by and large abide by NOCSAE standards. And that means their players are effectively forbidden from flapping.

Wait, Little Leaguers largely can’t wear this added piece of safety equipment in the name of — safety?

“That’s about the size of it,” says Herb Markwort, president and CEO of Markwort Sporting Goods, the small St. Louis-based company that manufactures C-Flaps. “With the legal atmosphere, Little League and Pony League and high schools and even the NCAA don’t want to be liable if they don’t adhere to the so-called NOCSAE rules and certifications.”

NOCSAE, an independent nonprofit, says add-ons to helmets mean they are no longer identical to the ones originally certified by manufacturers, potentially voiding safety certifications. And C-Flaps require drilling holes in helmets for three screws.

Robert Crow, a retired plastic and reconstructive surgeon, is the Abner Doubleday of the C-Flap. He cooked up the first one in his kitchen when he was a team doctor for the Atlanta Braves decades ago.

“I got some orthoplast, which is a splint material, from my orthopedic colleagues and started playing with a guard in my wife’s frying pan,” Crow says, “until one night I came up with a prototype.”

Crow had found that players who’d been beaned in the face didn’t like the bulky protective devices available for them to wear when coming back from injury. So he wanted to come up with a device that offered protection without impeding vision. He worked up a mold and had it tested at a lab at Wayne State University in Detroit. Then he worked on it some more.

Crow had players test it at spring training and by the mid-1980s felt he’d perfected it with a tough polycarbonate material. He got a patent in 1987 and called his device a C-Flap — for himself and for a part of the body his device protects. That’s C as in Crow, and C as in cheek.

Crow doesn’t remember which MLB player used it first in a game but Oakland A’s catcher Terry Steinbach was among the early adopters. The C-Flap’s coming-out party was the 1988 All-Star Game, when Steinbach hit a home run off New York Mets pitcher Dwight Gooden.

For most of the decades since, players wore C-Flaps when coming back from injury. That’s why Steinbach wore it 30 years ago. But in recent seasons, more and more players are wearing them to protect against getting hit in the face in the first place. That’s the case for Trout and Harper and the Milwaukee Brewers, who provide C-Flaps for the players in their farm system.

Markwort Sporting Goods, a family business that started with tennis equipment in 1931, bought out Crow in 2004. “We’d been buying C-Flaps from Dr. Crow so it made sense for us,” Markwort says. “But it wasn’t really a big seller for us for a long time.”

Markwort says for years C-Flaps made up about 1 percent of his company’s sales but that over the last three years sales have risen steadily to about 15 percent of the business. He says they are popular in South Korea, where he says they’re called “gladiator guards.” Markwort thinks the tipping point for the surge in sales came in 2014, when Giancarlo Stanton got hit in the face and suffered multiple facial fractures and dental damage.

Rawlings, the sports equipment manufacturer founded in 1887 — 100 years before Crow got his patent — is MLB’s exclusive supplier of baseballs and helmets. Rawlings currently buys C-Flaps from Markwort Sporting Goods and attaches them to helmets for players in the major and minor leagues who want them.

Guess who else wants them? Kids who see their heroes wearing them, of course. And that may happen soon.

Mike Thompson, Rawlings’ executive vice president for marketing, says the company is preparing to introduce a helmet model next month. The Mach Helmet, he says, will come with flaps pre-assembled. Another version, he says, will come with a helmet pre-drilled for what the company calls the R-Flap, as in Rawlings. He believes both versions will pass muster with NOCSAE.

“We’re going to have the Good Housekeeping seal of approval,” Thompson says.

Crow says he’s OK with a version called the R-Flap. “I can’t tell them what to do or not to do,” he says. “My patent ran its course and expired.”

Crow says he’ll watch the All-Star Game on TV. So what will he be thinking when he sees 10 All-Stars wearing the flap he first fashioned in a frying pan?

“Hopefully none of the guys get hit,” Crow says, “but if they do, that it does its job.”

For more, visit USA TODAY Sports