Curling is the darling of the Winter Olympics

What all that yelling in curling is about (1:02)

As the U.S. men's curling team goes for gold, Julie "Loudy" Foudy gets to the bottom of why they yell so much when competing. (1:02)

GANGNEUNG, SOUTH KOREA -- At a somewhat quiet morning of round robin play at the Gangneung Curling Center, the U.S. fan contingents scattered around the small arena lean forward, carefully watching Nina Roth cast the U.S. women's final stone in the ninth end of a tied (5-5) match against the Russians on Saturday. The end -- which is when each of the two teams cast all eight of their stones at the same target, called a house, before switching sides -- had not been going well for Team USA. "Wrong from the first stone," as someone sitting nearby put it, so escaping with a point and a lead going into the 10th and final end would be a real steal.

Roth, the U.S. skip, pushed off, casting a gentle draw shot almost exactly on the button. Chants of "USA! USA!" broke out, one after the other. An oddity of the curling audience here is that national team fans don't really sit together en masse, rather they gather in various groups scattered around the arena. The effect is that cheers, from fans of team Japan, say, will start from one contingent and then will be taken up by another group somewhere else in the venue, creating a sort of ongoing echoing process. Add four total games played simultaneously, multiplied by two teams a game, and the curling center can suddenly go from hushed to an aural cascade of multilingual, multi-intentional, multi-rhythmic celebration.

Roth woke up the arena again in the 11th end, this time with a mistake. The Russians had recovered a point in the 10th to draw the match at 6, requiring an extra end. Roth misjudged the weight on her final stone, casting it short, an error her teammates, Becca Hamilton, Tabitha Peterson and Aileen Geving sensed instantly. "It felt really good out of my hand, but then I saw the girls pound it," Roth said afterward. "They're great at judging and reading rocks, so they knew they had to pound it."

The three women swarmed in, sweeping the ice furiously to create warmth and decrease friction. Together, they just managed, inch by agonizing inch, to bring the 42-pound stone to rest just slightly closer to the target than the Russian's stone, giving the U.S. the point and the match.

"All I could do was yell at [my teammates], which I did," Roth said.

The evening sessions have been generally well attended and lively, especially when the Korean team is on the ice. But the more subdued morning matches are a good time to observe little details, ask questions of your neighbor, pick up some lingo and orient yourself to the yelling happening on the ice.

"The Korean crowds have gotten better and better since we started," said USA Curling CEO Rick Patzke. "I think at first a lot of people thought you had to be quiet the whole time. There was nothing but polite applause the first week, but now they know you can cheer all you want."

The charms of curling come through on TV, as well. It is relatable on television because it looks recreational instead of professional. The athletes are all miked up, which makes viewing seem like you're hanging out with the curlers, listening in on asides and fussing about tactics.

The temptation to armchair quarterback is irresistible. People start to imagine, "Hmm, I could do this, right?"

"Almost anyone can do it," Patzke agrees. "But," he adds, "almost anyone can golf too. There's a difference at this level."

In the United States, curling is still primarily a regional sport confined to the Upper Midwest or New England. The entire U.S. women's team -- Roth, Peterson, Hamilton, Geving, and the alternate, Cory Christensen -- hails from a total of three curling clubs in two states: Minnesota and Wisconsin.

But the geography and popularity of the sport is changing. There are now curling clubs in 47 states, and the number of curlers registered with USA Curling has more than doubled, from 10,000 to more than 22,000, since 2001, estimates Patzke, who watches each U.S. match here, agonizing over every stone, muttering tactical advice to himself and cursing under his breath when things are going wrong.

Patzke credits the 2002 Salt Lake City Olympics for curling's development in the United States. "Salt Lake was our coming-out party in America," he says. "NBC broadcast about 50 hours of curling. In Nagano in '98, it was like 30 minutes. The Olympics have definitely driven growth and exposure, but the key for us is not to disappear between Olympics. You can get really popular for 17 days and then go away, you know?"

For now, the trend is upward, especially on social media. Mr. T -- yes, Clubber Lang of "Rocky III" -- has received attention for his regular curling tweets since the games began. Hamilton's brother and U.S. teammate Matt Hamilton, one of the more popular curlers in Pyeongchang (at one match, a group of women chanted, "Matt, Matt, he's our man, if he can't do it, his mustache can!") tweeted at football players Aaron Rodgers and J.J. Watt, and they both tweeted their support in response. The Hamilton siblings went on "The Tonight Show Starring Jimmy Fallon," and during the mixed doubles, a debut event here at Pyeongchang, had a hashtag of their own: #HamFam.

"I can't even sift through all that stuff, the tweets, everything," says USA Curling's press officer Terry Davis. "We really want to capture this enthusiasm."