Fighting occurs when a player throws a punch or attempts to throw a punch in the direction of an opposing player. An instigator is a person who begins or encourages the action of fighting. There does not need to be any physical forceful contact or participation in the actual fight for someone to be considered an instigator.
Fighting, in general, is a major penalty that is given to all participants. An additional minor penalty is given to any player that starts or instigates a fight. If a player is considered to be an instigator of a later altercation, a game misconduct penalty will be imposed upon that player. These penalties are enforced in an effort to limit and potentially end all fighting that occurs in hockey games.
Fighting is technically an automatic penalty and any players involved in fighting are required to sit in the penalty box for at least 5 minutes. The referee has the freedom to determine the severity of the penalty and can even eject players from the game. One theory for why fighting is still allowed is that it is a way for the game to maintain order by policing itself and reminding players that there are consequences for violated rules. There is no one reason for why fighting is still allowed in the game today.
Fighting is usually not staged, but there have been instances where stage fighting has occurred. This is a hard action to regulate and the league along with individual GMs have made efforts to try to inflict stricter penalties for those who stage fights during games. For example, the NHL wants to impose stricter penalties for players that fight directly after a face-off as most of these fights are often unprovoked and staged.
Both fighting and instigating fall under the same umbrella, but you do not have to be a fighter to be a fight instigator. An instigator in an altercation can be involved in any of the following activities: traveling a distance to another player, taking their gloves off first, throwing the first punch, having threatening attitude or posture, verbal threats or taunting, and retaliating or retributing a prior incident. All of these activities demonstrate a player that is the aggressor of the situation, while a fighter may only be reacting to the instigator's actions.