Today when you walk into a professional sports venue, there's a good chance the facility is LEED certified. You may gain entry with a paperless ticket, watch your team play under energy-conserving LED lights, and catch replays on giant screens powered by solar panels. You might even chow down on grass-fed beef hot dogs and compost your leftovers.

When did the sports industry start to care about the environment? It's hard to pinpoint the exact moment, but the 2003 opening of Lincoln Financial Field—home to the Philadelphia Eagles football team—is a good place to begin. The team's owners asked NRDC to help them figure out how to reduce the stadium's carbon footprint, both during and after its initial build, and this changed the game for good.

Lincoln Financial Field, home to the Philadelphia Eagles football team Brad Feinknopf/OTTO

"It was really the first all-purpose sports stadium greening initiative, and I thought it was just a one-off," says Allen Hershkowitz, a former NRDC senior scientist who led the project. But at a board-member retreat the following year, he mentioned its success to NRDC trustee Robert Redford. "There was a panel discussion about reaching out to nontraditional allies," says Hershkowitz. "I said to Redford, 'I did this thing with the Eagles; maybe we should reach out to other sports teams.' His response was 'That's a great idea. What can I do to get it started?' "

Redford introduced Hershkowitz to Oakland Athletics principal partner Bob Fisher, another NRDC trustee, who encouraged Hershkowitz to pitch the commissioner of Major League Baseball. That meeting, which included an NRDC video narrated by Redford (a baseball icon, thanks to his starring role in The Natural), led to league-wide environmental efforts. The NRDC Sports Project, under the direction of Hershkowitz, was officially up and running.

Collaborations with the National Basketball Association, the National Football League, the National Hockey League, Major League Soccer, and the U.S. Open Tennis Championships followed. NRDC also launched its award-winning Greening Advisor, an online guide for teams looking to bring eco-intelligent practices to their venues and host community events like electronics recycling drives, local cleanup days, and tree plantings.

In 2010, the Sports Project celebrated a big milestone: Every major U.S. professional sport—basketball, football, hockey, baseball, and soccer—distributed NRDC-authored guidelines for bringing solar power to stadiums and arenas.

Solar panels in a parking area at Lincoln Financial Field Brad Feinknopf/OTTO

Riding on that momentum, Hershkowitz met in Seattle with staff members from the Seattle Seahawks, the Seattle Sounders, and the Portland Trail Blazers. The three pro teams, all owned by Microsoft cofounder Paul Allen, were already making individual efforts to recycle, reduce waste, and work with eco-friendly vendors, says Justin Zeulner, former sustainability director for the Trail Blazers.

"We realized that, working together, we could be a lot stronger and scale up our initiatives more than we'd been doing alone," Zeulner says. Having NRDC's support was critical, he adds. "It helped connect us with research about environmental best practices, so we could articulate what it meant and what the benefits would be. Without that leverage, I don't know if our vision would have gotten off the ground."

During that meeting in Seattle, NRDC and Allen's holding company, Vulcan Inc., formed the nonprofit Green Sports Alliance, or GSA. In 2014, Hershkowitz and Zeulner left their jobs at NRDC and the Trail Blazers to serve as president and chief operating officer, respectively, of the GSA, which has turned out to be one of the most influential collaborations of the environmental movement.

Green sports' impact, by the numbers

Within two years of its founding, the GSA grew to include more than 100 teams in 13 leagues; today it boasts a membership of more than 300 teams and venues. The alliance can take credit for hundreds of millions of pounds of carbon-emission reductions, millions of gallons of water conserved, millions of pounds of waste diverted from landfills, and tens of millions of fans enlightened by eco-focused public-service announcements both in stadiums and during TV broadcasts.

But Hershkowitz thinks a qualitative assessment of the GSA's accomplishments is even more powerful than a quantitative one. "The single most important thing we can do for environmental stewardship is change cultural attitudes about how we relate to the planet," he says. Sports, he adds, has been a way to connect with people and their passions: "Only 13 percent of people follow science, but 71 percent of people follow sports. A climate-change denier might attack scientists, but he's not going to attack NASCAR or Major League Hockey when their commissioners say that global warming is real and is an existential threat to their sport."

Lincoln Financial Field Stadium Brad Feinknopf/OTTO

Game plan for a winning future

While the GSA continues to focus on climate change and energy use, it has also taken up new causes. It's working with stadium vendors to offer antibiotic-free meat and more vegetarian options. It's also focusing on species preservation with its 2016 Mascots Forever initiative. "A report I started at NRDC found that about 60 percent of animal mascots are at risk of extinction," Hershkowitz says. "So now we have teams getting together to create a new platform for fund-raising and visibility."

The GSA is gaining international momentum as well, with members in 14 countries, affiliates in Europe and Australia, and a strong presence at the 2015 Paris climate talks. In 2015, Hershkowitz was named one of SportsBusiness Journal's 50 most influential people in sports. And for his early work with NRDC and the GSA, Major League Baseball commissioner Bug Selig received ESPN's Sports Humanitarian of the Year Award.

That type of recognition is huge, Hershkowitz says. He thinks back to 2008, when NRDC founder John Adams was invited to throw out the first pitch at a Boston Red Sox game. "I knew then that we had gone from being outsiders trying to change the system to being truly embraced by the system in the best possible way."