Do you ever scratch your head over the Department of Player Safety's decisions? Understanding a few key rules will make its logic far easier to follow.

Few topics polarize hockey's pundit populus and fan base like supplemental discipline, and for good reason. Plays that spark calls for suspension are dangerous and often result in major injuries. We should talk about them.

Common perceptions, specially among Twitter's most vocal fans, are that the NHL's Department of Player Safety struggles with inconsistency, that stars get preferential treatment, that there is no rhyme or reason to the league's decision making. That couldn't be further from the truth, however. During the 2014-15 season I visited the NHL DOPS war room and learned everything I could about how suspensions happen. I've spent the next couple years further brushing up on the subject, and I've realized the war between the fans and the DOPS stems primarily from one problem: lack of education.

It's not that we will or should agree with every decision the DOPS makes. Even its members have told me they don't want or expect that. It's just that we'll wring our hands over suspensions far less if we understand a few important rules and misconceptions. The next time you want to cry foul over a ban or lack thereof, consider these six pointers first.

1. AN INJURY DOES NOT INCREASE THE ODDS OF A SUSPENSION – ONLY THE LENGTH

Myth:"Mr. X is out long term, so that guarantees a suspension for Mr. Y"

Not even the most serious injuries, from a torn ACL to a broken back, impact a suspension if the NHL decides the play in question was not an infraction. Plenty of people called for a suspension on Zdeno Chara in 2011 when he drove Max Pacioretty into a stanchion, giving Pacioretty a broken vertebra and a major concussion, but it's the injury to Pacioretty that incited that emotional response. The league determined the play itself didn't violate a league rule.

An injury only impacts supplemental discipline if the league has decided the play in question indeed warrants a suspension. In that case, the injury will lengthen the ban.

2. A PLAYER'S PAST OFFENSES DO NOT INCREASE THE ODDS OF A SUSPENSION – ONLY THE LENGTH

Myth: "Mr. X is a repeat offender, so he'll be suspended for sure."

Repeat offenders earn the same treatment as injuries in that, contrary to popular belief, they don't increase the odds of a player being suspended. If the league determines a play in question isn't suspendable, the repeat offender isn't repeat offending, is he? Radko Gudas makes a perfect case study here. He has a history of getting in trouble with the DOPS, but this hit Oct. 3 on Jimmy Vesey wasn't deemed illegal, so his past transgressions had zero impact:

Then Gudas caught Austin Czarnik five days later with this hit:

The league did deem that hit illegal, meaning Gudas' history did factor in this time, and boom, six-game suspension.

As is the case with injuries, repeat offenses will impact suspension length only after the NHL decides a given play is suspendable. A guy doesn't gut suspended because he is a repeat offender. He gets suspended longer because he is a repeat offender.

3. WHETHER A PENALTY WAS CALLED ON THE PLAY IN QUESTION HAS NO IMPACT ON A POTENTIAL SUSPENSION

Myth 1:"Mr. X got a boarding major for that and was ejected. He's getting suspended."

Myth 2: "Mr. Y didn't even get a penalty for the play, so there's no way he gets suspended."

The DOPS operates independently from the NHL's officials and department of hockey operations. Calls made on the ice and subsequent disciplinary decisions have no impact on each other. That's why plenty of plays that earn penalties on split-second calls end up not earning suspensions from the DOPS. In such cases, the league decides (a) the infraction was minor enough that the call on the ice was sufficient punishment or (b) the call on the ice was wrong and that the play in question didn't even warrant a penalty. On the flip side, plays that earned no penalty at all can end up earning suspensions, as the league can decide officials simply missed an on-ice call or erred in not making a call.

The noteworthy exceptions to these rules, of course, are automatic suspensions, in which certain types of penalties and infractions (leaving the bench to start an altercation, three instigator penalties in one regular season, etc.) result in mandatory bans independent from the DOPS.

4. THE RULES OF SUPPLEMENTAL DISCIPLINE WERE AGREED TO BY THE PLAYERS IN THE COLLECTIVE BARGAINING AGREEMENT

Myth:"The league is afraid to hand out really long suspensions to stars"

Was Duncan Keith's six-game suspension at the end of last season for sticking Charlie Coyle in the face long enough? Yes and no. It was long enough relative to the rest of the bans handed out by the DOPS last season, as Keith got the second-longest. It was far too short in that every suspension is far too short. If you tripled Keith's suspension length to 18, he'd be a lot more careful with his stick going forward.

Why that's never going to happen: the rules of supplemental discipline are collectively bargained, meaning the NHL and its owners struck the deal with the NHL Players' Association. Everyone agreed to these terms. That means players and teams end up warring against themselves. The NHLPA, for example, would want justice for its member Coyle, but also a fair shake for its member Keith. We'll never see consistently long bans because the NHL's player population, which includes the perpetrators and the victims of all dangerous plays, wouldn't agree to it.

The DOPS operates within the confines of the CBA. Another place that factors in: dangerous plays for which the rules have not yet been invented. The most famous example is Matt Cooke's horrible, career-ruining hit on Marc Savard in 2010. The league's hands were tied at the time because Rule 48.1, illegal check to the head, didn't exist in its current form. Supplemental discipline could only be doled out within the confines of rulebook as outlined in the CBA at the time, so Cooke wasn't breaking a rule. The hit inspired a rule that polices similar hits today, of course. The point here is suspension decisions always have to operate within the rules and the CBA. If we don't like the rules, all we can do is change them later.

5. DEGREE OF FORCE AND 'GAME NARRATIVE' FACTOR IN AS SUBJECTIVE EVALUATIONS

To be clear, the DOPS isn't always right. One of the reasons why we won't always agree with its choices, even after we've educated ourselves on the rules, is the element of subjectivity. Two factors qualitatively evaluated would be the force of blows in question and the narrative of a given game. It appears Jake Virtanen won't earn any discipline for slamming Joakim Nordstrom's head into the boards Sunday night. The blow, while it looks bad, wasn't overly forceful. Nordstrom's body sliding on the ice before the shove is what produced the momentum. We can scoff at that line of thinking, but it helps to understand it, right? Game narratives play a role, too. If a hit that teeters on the brink of legality occurs between two players who were jawing at each other all game, or as a retaliation to an earlier play, it's more likely to be treated as predatory.

6. THE LEAGUE RULEBOOK HAS ALL THE ANSWERS

Myth: "Mr. X hit Mr. Y in the back. Automatic suspension."

Just give the ole rulebook a thorough read – here's a link to last year's – and it's far easier to understand why some seemingly dirty hits aren't treated as such by the DOPS. Gudas' hit on Vesey didn't earn a ban because Vesey turned at the last second and put himself in a vulnerable position. The hit arguably isn't even a penalty. It's right here in the league rules, under Boarding – Rule 41.1:

The onus is on the player applying the check to ensure his opponent is not in a defenseless position, and if so, he must avoid or minimize contact. However, in determining whether such contact could have been avoided, the circumstances of the check, including whether the opponent put himself in a vulnerable position immediately prior to or simultaneously with the check or whether the check was unavoidable can be considered.

Hopefully this mythbusting session helps. Keep fighting the good fight and keep questioning any play you think warrants supplemental discipline – but do so armed with an educated opinion. It's better for all of us.

Matt Larkin is a writer and editor at The Hockey News and a regular contributor to thn.com. For more great profiles, news and views from the world of hockey, subscribe to The Hockey News magazine. Follow Matt Larkin on Twitter at @THNMattLarkin