Hockey is a remarkably fast-moving game -- and it's only getting quicker. Officiating that game in real time is no easy task.
"The refs are doing as good of a job as they possibly can," Ottawa Senators defenseman Erik Karlsson says. "I don't think I could ref or do as good as job as they are, and I don't think we give them enough credit for how difficult it is to make those decisions with the speed we're going."
It still seems like some rules are more difficult to regulate than others. In the NFL, the catch rule has been a cause for debate for the past three years, as many players argue that rulings on the act of possession are both subjective and wildly inconsistent.
Before the season, ESPN.com asked several NHL stars to name the equivalent in hockey. What is the hardest -- and perhaps the most subjective -- rule for NHL refs to call? Here's what they said:
Offside
Arizona Coyotes center Max Domi: Offside, especially now with the whole challenge thing. [The NHL has increased the penalty this season for teams that unsuccessfully challenge whether a player was offside before a goal. Instead of losing a timeout, the team is hit with a delay-of-game penalty.] That's the worst, when you're going down [the ice] and the offside happens and you still have the puck for like 20 seconds. I don't know what the full rule is, but if something like that happens, and obviously the offside has nothing to do with it, but the goal gets called back you're just like, "Are you kidding me?"
Chicago Blackhawks winger Patrick Kane: The offsides rule. Sometimes after the review, you don't even know if the guy is offside or onside. I would say the [subjective part] is kind of like having control of the puck on the offside.
Columbus Blue Jackets defenseman Seth Jones: Offsides has probably been that [NFL's] catch-no-catch-kind of rule, that they can take back a goal or whatever it is.
Dallas Stars center Tyler Seguin: Offside. Especially with the cameras and everything. And especially with the ones that are dealing with a goal. It's very subjective.
Washington Capitals winger T.J. Oshie: It's probably the offsides call. There is a gray zone there, and I feel like the gray zone might be a little too big.
Slashing
Calgary Flames winger Johnny Gaudreau: Slashing. Tapping, slashing. I broke a finger [because of] it. But it's tough for the referees. You don't know whether it's a love tap, you don't know if it's a slash. It's part of the game, and the game is going so fast it's hard to cut down on the slashing call like that.
Goalie interference
Buffalo Sabres center Jack Eichel: Goalie interference is tough. You don't know if it's intentional or unintentional. You don't know whether they wanted to get pushed in by the defenseman or if they stayed out of the crease. So it's a tough rule.
Vancouver Canucks defenseman Chris Tanev: Goalie interference. It's sort of hit-or-miss depending on the day.
Other tough calls
Anaheim Ducks center Ryan Getzlaf: Impeding progress is a hard one to handle. When guys chip the puck in, and d-men finish them or skate them off or whatever they're doing, that one always seems to be hit-or-miss every night.
Minnesota Wild center Charlie Coyle: Goals off the foot. What's a distinct kicking motion? It's hard to decipher, you know? Those are tough things.