On April 16, the creator of a parody Twitter account called “BenSmithsDad” got an ominous phone call. It was the culmination of an odd sequence of events: Two and a half years before, he’d become an avid practitioner of CrossFit, the grueling workout craze. In November 2012, he'd created the account for laughs, a way to mock a buddy who had lost to Ben Smith, a top athlete in the regionals of the fitness regimen's global competition, the CrossFit Games. But the inside joke of an over-the-top CrossFit obsessive had attracted a wider following (plenty of CrossFitters knew the type), and soon BenSmithsDad was posting about slamming beers and banging out back squats to an audience of thousands on Twitter and Facebook. Then, on April 15, he went too far. That day two bombs went off at the Boston Marathon, killing three people, including an eight-year-old child. Bensmithsdad had turned it into a macho fitness joke.

"Maybe the Boston Marathon just wanted to be more like the Tough Mudder and decided to throw in a couple obstacles at the finish to spice things up,” he posted. “Adventure Races are all the rage right now.” Even regular fans complained.

The voice on the other end of the line was from CrossFit’s media offices. The message was polite, but matter of fact. BenSmithsDad should post an apology to Ben Smith and his family. Then he should delete his accounts and remove the character from the Internet. If he refused, sooner or later his real name would become public. Probably sooner. A film crew might even show up at his office.

Later that day, an eerily specific email arrived from CrossFit’s Director of Training, former Navy SEAL Team 6 member Dave Castro. “I would really like to meet you,” Castro wrote. “I can drop in your [office name] in your [city] or even your box"--the CrossFit term for a gym. "I would love to put a face to the name.”

Spooked, BenSmithsDad cried uncle. "I’m done with it,” he told me via phone. (He requested to be kept anonymous, for fear of upsetting his employers). "I was just doing this for laughs, I have nothing to gain from it." Still, he marvels at how aggressively CrossFit responded. “What other business on earth would do that?”

CrossFit Inc., the company behind the push-it-to-the-limit fitness program, has a social media strategy as intense and as brutal as its workouts. Most of the time, the five-person social media staff plays happy shepherd to a devoted online flock: They post workout routines to the Crossfit.com homepage, celebrate athletes’ achievements on Facebook, and upload exercise videos to YouTube, where the company's channel has more than 212,000 subscribers--more than twice as many as Nike. But when someone criticizes the CrossFit methodology, misstates its goals, or mocks its athletes or coaches, the company unleashes its enforcers. These are two men, Russell Greene and Russell Berger, known around the CrossFit media office as “The Russes.”

Greene and Berger are longtime CrossFit loyalists. Greene, 26, started doing CrossFit workouts he found online at age 14, struggling alone at the local YMCA. Berger, 27, learned about CrossFit while in the Army's 75th Ranger Regiment, then opened his own CrossFit box after he left the military. Now working full-time at the CrossFit offices in Scotts Valley, California, the Russes fight its social media battles big and small, from an effort last summer to ward off a takeover bid from a venture capital firm, to more mundane matters. They argue on Internet message boards. They call into weight-lifting podcasts. On Wikipedia, they brawled so aggressively over changes to the website's CrossFit entry that their office's IP addresses got banned from editing the site. And BenSmithsDad? There have been other BenSmithsDads.