Though many see it as a modern problem, the hockey fight has been part of the game since the rules of the sport were first written in the 1800s.
The NHL issues long suspensions for extreme on-ice assaults.
But those penalties usually apply to players who attack with their sticks, or those who go after an unwilling or unaware opponent.
A fistfight between two willing combatants has long been accepted as a "natural" part of hockey and a tactic for motivating team mates and intimidating opponents.
With so many players moving at high speed and competing for the puck in a confined space, collisions and struggles to establish body position were a part of ice hockey from the start.
The physical game also appealed to spectators and many players, and it was allowed to thrive.
Body-checking and other elements of the physical battlwe were written into the early rules.
When some players crossed the line from aggression to violence, spectators cheered and authorities didn't act to eliminate such tactics.
There's little evidence to suggest that the NHL or other hockey leagues seriously considered extreme measures like forfeited games or season-long suspensions to discourage fighting.
The Five-Minute Penalty
The first NHL rules against fighting were introduced in 1922, and set a standard that continues to this day.
Rather than opt for automatic ejection from the game, the league decided fighting should be punished with a five-minute penalty.
"Taking Care of Business"
The "Original Six" era saw fighting established as an ordinary part of the NHL game.
In history books you will find recollections of many infamous fights, such as a memorable bench-clearing brawl at Maple Leaf Gardens on Christmas night, 1930.
The 1936 Stanley Cup Final featured another unforgettable fight night, with the Red Wings and Maple Leafs charging from their benches for a brawl.
Many stars of the post-war era, like Gordie Howe, Bobby Orr, and Stan Mikita, were known for their ability and willingness to "take care of business."
Fighting came to be understood as a useful tactic: a way for players to prove they wouldn't be intimidated, and as a direct challenge to the courage and commitment of opponents.
The Goon Emerges
The 1970s were a turning point for the role of fighting in hockey, and the debate over it.
Two of the best teams of the decade, the Boston Bruins and Philadelphia Flyers, used fighting and intimidation as core tactics.
The 1970s also saw the evolution of the "goon" or "enforcer."
Prior to the enforcer era, just about any player might fight under the right circumstances.
But when a team like the Flyers brought in a fighting specialist like Dave Schultz, other teams responded in kind.
The staged, premeditated fight was commonplace, amd designated "tough guys" were soon found on most NHL rosters.
Bench-clearing brawls are among the most famous images of the 1970s, and network television coverage helped make fighting a trademark characteristic of the pro game.
In 1977, the NHL ruled that any player joining a fight in progress (the "third man in") would be ejected from the game.
Ten years later, the league decided that a player leaving the bench to join a fight would be subject to a 5-to-10 game suspension.
The Instigator Rule
While new rules ended the embarrassing spectacle of the bench-clearing brawl, the one-on-one hockey fight remained as popular as ever.
NHL rules were further tweaked in 1992, with the introduction of the "instigator" penalty.
This imposed an additional two-minute penalty and game misconduct on any player deemed to have started ("instigated") a fight.
In practice, the instigator penalty is rarely called.
Referees tend to decide that most fight are started by agreement of both parties.
The instigator penalty is controversial.
Many believe the rule actually encourages dirty play, by preventing enforcers from properly "policing" the game.
According to this argument, the threat of a fist in the face is a deterrent against dirty tactics like elbowing and high-sticking.
But if the enforcer doesn't want to hurt his team by taking a two-minute penalty and a misconduct, he will be reluctant to step in. So the dirty player roams free.
The Fighting Debate
Opposition to hockey fights has grown more vocal since the 1980s, with medical experts, legal authorities, journalists, and others calling for more severe punishment.
They argue that fighting drives too many spectators away from the game, and discourages many children who might otherwise play minor hockey.
Increasing awareness of concussions and other head injuries has brought the fighting debate to new levels.
Opponents of fighting argue that it's hypocritical for the NHL to take measures against head shots and concussions, while still tacitly encouraging players to punch each other in the head.
Those opponents have been encouraged by long-term trends, which show a slight decline in the number of NHL fights, and the decline in the number of players who do little except fight.
Outside the NHL and other North American pro leagues, fighting has long been discouraged.
But support for fighting as an essential part of the game remains high among fans, NHL players, NHL managers and coaches, and many others in the hockey community.