Slap Shot

Reggie Dunlop (Paul Newman) is the aging player-coach of the Charlestown Chiefs hockey team in the fictional Federal League. A perennial loser for years, the team's manager Joe McGrath (Strother Martin) has resorted to extreme cost-cutting techniques and embarrassing promotional antics to keep local interest alive. Dunlop, while not particularly talented as either a player or coach, is a skilled con man, and regularly manipulates the team to his own advantage. During a hopeless season, the Chiefs pick up the Hanson Brothers, bespectacled violent goons with childlike mentalities, complete with toys in their luggage. Horrified at being given players who seem stupid, immature, and unreliable, Dunlop initially chooses not to play them.
When it is announced that the local mill will be closing and 10,000 workers will be unemployed, Dunlop grows concerned about the team's future. He makes several attempts to learn the identity of the team's anonymous owner (a running gag throughout the film), but is deftly deflected by McGrath each time. When McGrath accompanies them on an away game, top scorer Ned Braden (Michael Ontkean) overhears him attempting to get a job with another team. After Braden relays this information to his teammates, Dunlop confronts McGrath, who confirms that the Chiefs will fold at the end of the season.
Determined to save the team at all costs, Dunlop starts provoking fights at games to secure goals and the Chiefs start to win games. In a moment of desperation, he lets the Hansons play and discovers that their aggressive fighting style enthralls the fans. He begins retooling the team as a goon squad in the Hansons' image and attendance quickly increases. Capitalizing on this growing interest, he plants a false story with eccentric sports news writer Dickie Dunn (M. Emmet Walsh) that a Florida retirement community is interested in purchasing the team, in order to bolster the confidence of the players and to hopefully inspire an actual sale.
Most of the players, such as Dave "Killer" Carlson (Jerry Houser) embrace the shift, but Braden, a college-educated player with a clean style, resists every chance to fight. This eventually leads to Dunlop benching him. Braden's failing relationship with his bored wife Lily (Lindsay Crouse), puts further strain on him, and Dunlop feigns interest in her to make Braden more aggressive. After realizing that she is truly depressed and falling into alcoholism, Dunlop establishes a friendship between Lily and Francine (Jennifer Warren), Dunlop's ex-wife.
Meanwhile, the Chiefs' tactics get them into a great deal of legal trouble and make them a number of enemies, in particular, the Syracuse Bulldogs and their mercurial leader Tim "Doctor Hook" McCracken, who is determined to pummel Dunlop after a humiliating defeat. When the Chiefs' success fails to make any real progress, Dunlop's patience wears out. He uses an embarrassing past homosexual advance from McGrath to blackmail him into revealing the identity of the team's owner: a wealthy widow named Anita McCambridge (Kathryn Walker). Amused at Dunlop's optimism, she compliments him on his clever manipulations, but admits that she cares little for hockey and despises the violence. She informs Dunlop that while he has made the team a viable commodity for a lucrative sale, she would rather fold it to procure a tax write-off. Appalled at her indifference, Dunlop insults her and storms off. Completely defeated, and with the realization that the championship will be his last game, Dunlop decides to abandon his efforts and end his career with a clean win. He admits his deception to the players and manages to get them on board to play their final game straight: "old-time hockey."
The Syracuse Bulldogs, the Chiefs' opponents, have abandoned their original lineup except for McCracken and stocked their roster with an assembly of the most notorious enforcers in Federal League history, some of whom have actually been banned from the sport but reinstated for this one occasion. The Chiefs are pummeled in the first period, and McGrath storms into the locker room and angrily informs them that the stands are full of NHL scouts. Hearing this, Dunlop and the Chiefs change their minds and turn the remainder of the game into an all-out brawl.
While sulking on the bench, Braden spots Lily in the stands with Francine. Enthralled by her makeover and attendance, he skates out to center ice and strips off his uniform, prompting the arena's band to accompany him with "The Stripper." Both teams stop fighting and stare in amazement at the striptease, more offended by Braden's antics than their own. McCracken demands that the referee put a stop to it. When the official refuses, McCracken sucker-punches him, causing the referee to declare a forfeit, thus giving the Federal League championship to the Chiefs. The team celebrates by parading around the ice with the championship trophy, carried by Braden, wearing nothing but skates and a jockstrap.
During a championship parade in Charlestown the following day, Dunlop flags down a departing Francine and informs her that he has accepted a job as the coach of a new team, the Minnesota Nighthawks, and that he intends to bring Chiefs players with him. She bids him goodbye and drives off, and he is left claiming to Braden and Lily that she will be coming to Minnesota "for sure."

Question: What does McCracken do that causes the referee to declare a forfeit?
Answer: sucker-punches him