Steve Downie has been a very bad boy. The Tampa Bay Lightning’s winger barreled down the “slot” in front of the Washington Capitals’ net like a crosstown bus, plowing into and over Semyon Varlamov, the Caps’ goalie. In the National Hockey League, this kind of thing just isn’t tolerated. It’s an affront, a provocation, an invitation to violence. Someone would have to reply.

Racing Downie up the ice, Matt Hendricks, the Capitals’ forward, caught him along the boards near the corner. With a hard check, he pinned Downie against the wall. Downie reciprocated with a low forearm. As the crowd at Verizon Center rose with swelling anticipation, it was on. The two men wrestled in a confusion of sticks and gloves, skates slip-sliding beneath them. Hendricks swung, landing the first and decisive blow, an uppercut that snapped Downie’s head back. Stunned but not incapacitated, Downie grabbed the nape of Hendricks’s jersey and tugged, momentarily turning his adversary into a flailing, headless turtle. Downie rained blows, but Hendricks, swinging blindly, miraculously connected with a couple of jabs. Within moments, the two angry players were in a pile on the ice, immobilized by officials. The altercation was over.

As pro-hockey fights go, Downie vs. Hendricks in early January wasn’t especially brutal or memorable. No one had his face split open or his teeth dislodged. Nevertheless, the punch-up presented a vivid illustration of the NHL’s code of vigilante justice. Downie trespassed; his payback was swift and righteous. As Hendricks skated to the sidelines to serve an obligatory five-minute penalty for fighting, his teammates tapped their sticks on the ice and boards, offering him the game’s equivalent of a 21-gun salute.

All in a day’s work for Hendricks, a modest Minnesotan whose comportment off the ice is as mild as his scrappy, sandpaper persona on it. Hendricks played 301 games in hockey’s minor leagues, doggedly hoping to parlay skill and hustle into an NHL career. He came close to the big league several times and stuck for one long stretch last season with Denver’s team, the Colorado Avalanche. But by last summer, the Avalanche was no longer interested. Hendricks was 29 years old. His professional hockey dreams were flickering like a dying candle.

“What’s it going to take?” he wondered aloud to his former Colorado teammate, Cody McLeod, during a golf outing last summer.

Many months later, Hendricks still remembers McLeod’s answer: “Matt, you’ve got to start fighting more.”

***

Hendricks came into the Capitals’ training camp last summer as a long shot. The team’s general manager, George McPhee, a scrapper himself in his playing days, offered him a 30-day tryout contract, little more than a chance. He stuck, impressing McPhee and Capitals coach Bruce Boudreau by scoring three goals in his first exhibition game. But it was Hendricks’s willingness to give and take lumps on the ice that truly suggested he was a keeper.

Through 74 games this season, Hendricks has been in 14 fights, the most on the team and 10th most in the NHL. This has helped earn him a team-leading 106 penalty minutes. During one four-day stretch in December, Hendricks fought three times, including twice in a game against the New York Rangers. He has fought at home and on the road, in preseason and even in intrasquad games. In the Avalanche’s training camp two years ago, Hendricks had six fights in 14 days, two with teammates, including one with his roommate. At the end of the Capitals’ training camp, the team signed him to a one-year contract worth $575,000.

“He was like a missing part of the puzzle for us,” Boudreau says one morning after a practice at the Caps’ Arlington training facility. “It’s never about him. It’s about the team. He’s the consummate pro. He knows when this team needs a lift, and he’s willing to do what it takes.”

Hendricks is no “goon,” employed merely for his ability to clobber opponents. He’s a playmaker and stout defender, too, and has proved that he can score (he had eight goals and 15 assists as the Capitals headed into the playoffs, solid totals for a player on the fourth line, or rotation). Teammates laud his tenacity and toughness. Right winger Mike Knuble, a 15-year NHL veteran, describes Hendricks as “blue-collar” — sports-speak for hardworking, self-sacrificing, unheralded.

Yet it has been Hendricks’s willingness to fight — to “drop the gloves,” as hockey people say — that has been his value-added, his competitive advantage. “I wanted to find something I did and I do that’s different from the other players,” he says one afternoon. “Something that I could contribute.”

If a willingness to take and give a beating sounds like an unusual job description, it pays to know a few things about the NHL. Fighting is as old as the 94-year-old league and has a rich and complex history. Rule changes over the decades have taken some of the savagery out of the mayhem (the bench-clearing brawls of the 1970s are extinct, for example), but it’s still an integral part of the game. In North American professional hockey, fighting has strategic value. A fight can shake up a losing team, intimidate an opponent or swing a game’s momentum if it’s well timed. Yes, well timed. Though casual fans may not realize it, most NHL fights are premeditated and usually have a very specific purpose.

They’re also very, very painful. From afar, Hendricks’s face appears as smooth as a freshly tended rink. Close up, the nicks and knots — the traces of his calling — are more evident. Just beneath his right eye is a fading souvenir from an encounter in December with Sean Avery, the Rangers’ chief antagonist. It took a half-dozen stitches to close that gash; Hendricks’s blackened and bloodshot eye healed on its own. His hands usually hurt for days after a fight. Almost a week after his last fight, he turns his right hand over and lays it flat on a table. The knuckles above his pinkie and middle finger appear to have been mashed by a hammer.

Last season, Hendricks suffered a concussion in a fight with Brad Staubitz, then of the San Jose Sharks. Hendricks missed just four games. Some weeks earlier, in a preseason game, Hendricks went at it with Wayne Simmonds of the Los Angeles Kings. Simmonds threw a bomb that caught Hendricks’s nose, shattering it. The punch dropped him to the ice, leaving it spattered with his blood. Hendricks didn’t miss any games that time.

“It’s not the most fun job in the world,” he says, shrugging. “I like it when it’s over. I like what my teammates say when I’m done. They know I’m doing it for them. You have to be willing. You don’t do it for personal gain. ... It’s what I have to do to play in the NHL.”

The fact is, Hendricks — “Hendy” to everyone on the Caps — fights so his teammates don’t have to. Fighting in the NHL is as much about protection and preemption as about payback. It follows a simple logic: Cheap-shot a player — say, Alex Ovechkin, the Capitals’ superstar left winger — and you’ll hear from Hendricks or the Capitals’ other battlers, Matt Bradley and D.J. King. Players like to say fighting “cleans up the game,” meaning it avenges underhanded play and keeps it from becoming even more chaotic. Violence, in other words, becomes the means to deter more violence.

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Fighting is against the rules in the NHL, but that’s not to say it’s outlawed. Alone among the major professional team sports, the NHL essentially tolerates and manages it. Whereas pro baseball, basketball and football hand out stiff fines and suspensions for brawling, hockey combatants merely serve five-minute penalties (sometimes more if their behavior is deemed especially egregious). Fighting is actually honorable, the ultimate in taking one for the team.

Fights are rare in college and in Olympic and European professional hockey because the consequences — ejection, suspension — are prohibitive (critics say that just makes dirty play sneakier). But the NHL and its farm system of minor leagues have been reluctant to impose such penalties. Despite growing evidence that hockey’s brawlers risk serious long-term brain damage, despite rare but shocking episodes such as the death in 2009 of a minor-league player, Don Sanderson, following a fight and a fall, the NHL says it doesn’t plan to change anything. “We believe it’s a safety valve that prevents worse from happening on the ice,” NHL spokesman Frank Brown says.

The league’s commissioner, Gary Bettman, has carefully walked a not-condemning/not-condoning line for years. “I don’t think that there’s any appetite to abolish fighting from the game,” he told the Associated Press after Sanderson’s death, “and there are lots of reasons for that, including the fact that it’s been a part of the game.” (Bettman declined several requests for an interview for this story.)

You don’t have to be much of a cynic to suggest the real reason the league looks the other way: Fighting is good for the NHL’s bottom line. Fighting is to the game what car wrecks are to NASCAR — a visceral, guilty thrill for fans. Some teams play up the entertainment value of fights, cranking up tunes such as “Macho Man” and “Enter Sandman” during the action.

“When I go to a hockey game, I look forward to seeing a fight, and I enjoy it immensely. ...” sportswriter Frank Deford confessed a few years ago. “I know I shouldn’t, but I do. It brings out the worst in me. Apparently, this makes me a very typical hockey fan.” In fact, surveys of fans have consistently shown high levels of support for fighting; in a 2009 poll, 63 percent of Canadian fans said they were against banning it. Added Deford: “The NHL won’t give up fights to please critics for the same reason that strip shows won’t give up naked ladies. You gotta play to your constituency.”

Hockey fights are so enduring, and so popular, that an entire subculture has grown up around them. Homemade VHS tapes of the best ice brawls and the meanest “enforcers” started circulating in the 1980s. Before long, the NHL got into the act and marketed its own “best of” videos. Nowadays, fight clips abound on the Internet. Connoisseurs flock to sites such as Dropyourgloves.com and Hockeyfights.com, where fights are rated and dissected, and clips are archived like precious artifacts.

“Fighting is a very visual indicator of the players being emotional about the game,” says David Singer, founder and proprietor of Hockeyfights.com, which started in 1999 and now attracts, by Singer’s count, about 500,000 unique visitors a month. “You don’t get that in other sports. A good fight gets you out of your seat just as a great goal or save does. Maybe even more so.”

Although some fights start from a spontaneous combustion of emotions, in a flash of irritation or frustration, many don’t. Typically, they begin in almost dainty fashion — with an invitation. Hendricks will ask another player, or be asked by one, to square off with four words: “Do you wanna go?”

This kind of etiquette is necessary because of a rule instituted by the league in 1992. The “instigator” penalty tacks an additional two minutes in the penalty box to an aggressor, giving the “victimized” team a major advantage. But the ask-and-accept system assumes both parties are willing combatants. A player, after all, can decline an invitation to fight because of injury or if he sees no tactical advantage for his team.

These rules — pro hockey’s unwritten “code” — add a layer of quasi-civility to the business of brawling. Among other things, the code prohibits fighters from biting, hair-pulling or head-butting. It frowns on players fighting during line changes, the period of rapid player substitution, because one party may be too winded and thus at a disadvantage. It looks down on big guys, so-called heavyweights such as the Caps’ D.J. King, from taking on smaller players (Hendricks is a middleweight). Would-be fighters don’t wear visors, either. Visors are considered disrespectful among the fighting fraternity because an opponent might hurt his hand by striking one.

What’s it like to fight, to swing at another man and be swung at by him in front of thousands of excited people? Even after dozens of fights, Hendricks describes the experience as something of a blur, an almost primal and instinctive series of movements. A rush of adrenaline and aggression. A flash of fear. “Once the fight starts, I seem to go blank,” he says. “Sometimes, I need to actually watch the fight just to remember what happened. I think it’s almost like I’m blacking out and just doing what you do.”

Preparation and foreknowledge are important. Hendricks has taken fighting lessons and has trained on heavy punching bags. Days before a game, he’ll study videos of likely adversaries, sizing up their strengths and tendencies (left-handed? right-handed?). He knows who’s likely to demand a fight from him, too. Knowing when to fight — will it help the team now or later or not at all? — “might be more important than the fight itself. When it comes to fighting, this was the hardest lesson to learn,” Hendricks says.

Kim Hendricks, Matt’s wife, says her husband’s methodical preparations are an extension of his personality. “He’ll come home before a game and go to the computer and study the other guys. He doesn’t go out there just to beat someone up. He waits for the right guy and just the right point in the game.”

After accompanying him on much of his journey through the minor leagues — after college, Hendricks played for teams in Milwaukee; Lowell, Mass.; western Florida, Rochester, N.Y.; Hershey, Pa.; Providence, R.I.; and Cleveland — Kim Hendricks has seen enough hockey to appreciate her husband’s skills and particular niche. She has even made a tentative peace with fighting. “I think if you had asked me about it two years ago, I would have said, ‘Oh, my God,’ ” she says. “Especially this year, with the facial lacerations, the black eyes. There was a time when he didn’t go three days without having a bruise or stitches. I’m used to it now, but we go to dinner, and you see everyone staring at him. We went to a grocery store, and there was this one kid, he was so afraid he was holding on to his mom.”

Like Kim, Matt’s father, Doug, appreciates what it took for his son to make it to the NHL, even if he’s not entirely comfortable with the bare-knuckles aspect of it. “It’s kind of hard to watch,” says the elder Hendricks, a former Marine. “But I know it’s what he has to do. Matt’s always been a very tough kid. I know he doesn’t like it, and I know I don’t like it, either. You just have to hope for the best and put in a little prayer.”

The irony of Matt Hendricks’s role on the ice is that there’s not a hint of the street tough about him outside the arena. Watch him after practice some day. When a scrum of fans descends on him for autographs and photos one afternoon outside the Caps’ practice facility, Hendricks happily and patiently obliges every request. Kim Hendricks says she has never seen a “macho, tough-guy side” to her husband. At home, she’s the volatile one; he’s more likely to avoid confrontation.

Nor is Hendricks an especially intimidating physical presence. The Capitals list him at 6-foot even, but that may be a polite exaggeration. His official weight is 215 pounds, but that, too, seems optimistic, especially after a long season.

Hendricks was selected by the Nashville Predators in the fifth round of the 2000 NHL draft as a high school senior but chose to attend college instead at his parents’ urging. After four years at hockey-mad St. Cloud State University in central Minnesota, one of the key stops in his minor-league odyssey was Hershey, where Hendricks played for Boudreau, then the coach of the Capitals’ American Hockey League farm team, the Bears.

Boudreau became a mentor; Hendricks calls the talkative coach “a father figure” who offered criticism as well as encouragement. Boudreau told him he had what it took to play in the NHL. “What that does for you is hard to describe. It’s so much,” Hendricks says. “You start believing in yourself a little more. You work harder. You push.” Doug Hendricks says Boudreau was one of only three people who believed his son could make it to the highest level; the other two were Matt’s agent and Doug Hendricks.

***

The long-term effects of fighting in hockey aren’t well understood, but even without brawls, the game is brutal enough. Concussions from collisions and hard hits have ended the careers of many top players and have kept players such as Pittsburgh Penguins star Sidney Crosby on the bench for long periods this season.

Fighting, however, appears to add to the risk of brain damage. Researchers at Boston University’s medical school have recently found evidence of a degenerative brain disease in postmortem brain samples of two legendary hockey brawlers, Reggie Fleming and Bob Probert. The disease, called chronic traumatic encephalopathy, is the same as that found in more than 20 deceased NFL players, which has spurred calls for better football helmets and other protective changes.

The revelations about Fleming and Probert are too limited to suggest broad conclusions about hockey fights, because other factors — genetic predisposition, substance abuse, car accidents — might have contributed, says Robert Cantu, a neurosurgeon who helped conduct the Boston University research. Researchers hope someday to study the brains of “skill” players such as Wayne Gretzky, who rarely fought during his long career, to get a better understanding.

Still, for now, “the obvious thing is to reduce all unnecessary head trauma” in games and practice, Cantu says. Getting rid of fighting would be a start, he says: “It’s not necessary. If the game is properly officiated, you don’t need [fighting]. It doesn’t have to be a part of ice hockey.”

Boudreau, for one, dismisses the long-term health risks as “something you media guys make a big deal about.” Hendricks simply shrugs: “This is the lifestyle I chose to live, and I love it. I don’t have to do it. I could go get a 9-to-5 job, but that’s not what I want. I’ve worked for this since I can remember. I think worrying would only shorten my career.”

In February, in the midst of his best season ever, Hendricks signed a new deal with the Capitals, a two-year contract worth $1.6 million. Even so, Hendricks recognizes that he can’t coast. He knows there’s someone else coming along willing to do whatever it takes, including dropping the gloves. Someone, in other words, just like him. For the rest of his hockey career, Matt Hendricks knows the truth about his hard-knock life: He’ll always be fighting for his job.

Paul Farhi is a Washington Post staff writer. He can be reached at farhip@washpost.com