Why the NHL hesitates to use trusted goal-line cameras

HostWe have all been there, leaning in toward the screen, staring at a blurry replay while the refs huddle up on the ice. It feels like every other sport has a magic eye that knows exactly where the ball is, but in hockey, we're still guessing and squinting at shadows. Why is it so hard to just put a camera on the line and get a clear answer?

GuestIt's a lot harder than it looks because hockey is basically played on a giant mirror. If you look at soccer or tennis, you have a bright ball moving against a flat, dark green background. The cameras can track that easily. But in hockey, you have a black puck flying across white ice. That ice reflects every light in the building. To a computer, the real puck and the reflection on the ice look almost the same. If a camera tries to track the puck at a hundred miles an hour, the glare from the ice makes the puck look like a smear or even a ghost.

HostBut we have chips in the pucks now, right? I see the stats on the screen telling me how fast a shot was or how far a player ran. If there's a chip inside the rubber, why can we not just use that to tell if it crossed the line?

GuestWell, the chip is right in the middle of the puck. That works great for tracking how fast it moves through the air, but it's a nightmare for the goal line. For a goal to count, the whole puck has to cross the whole line. If the puck is flat on the ice, the chip tells you where the center is, and you can guess where the edges are. But pucks don't always stay flat. They tumble, they flip, and they stand up on their sides. If a puck is leaning at an angle, the chip in the middle might be past the line, but the bottom edge might still be touching it. A few millimeters make the difference between a win and a loss, and the tech just isn't sharp enough to be that sure yet.

HostI still find that hard to buy. We can land a rover on Mars, but we can't tell if a piece of rubber went two inches past a red line? Tennis can tell if a ball hit a tiny sliver of a white line from across the court. Is a puck really that different from a tennis ball?

GuestIt really is. A tennis ball is a sphere, so no matter how it spins, it looks the same to a camera. A puck is a disk. When it starts flipping, its shape changes constantly from the camera's point of view. It goes from a circle to a thin line and back again. Plus, in tennis, the ball is usually out in the open. In hockey, you have a goalie, two defenders, and an attacker all falling into the net at the same time. There's a pile of legs, gloves, and sticks covering everything. If the puck is tucked under a goalie's leg, the camera can't see it. If the camera can't see it, it can't track it.

HostSo the cameras in the goal posts aren't enough? I see those angles all the time during reviews, and they seem to show the puck most of the time.

GuestThose cameras are great for us to watch, but they have a big flaw called the parallax effect. It's an optical trick. If you look at the goal line from an angle, a puck might look like it's past the line when it's actually hovering right above it. To be one hundred percent sure, you need a view from directly above. But when you look from the top down, you usually see the top of the goalie's head or his glove. The NHL has been testing a system with about fourteen high speed cameras around the rink to try and solve this. They want to create a 3D map of the puck in real time, but even then, the system can lose the puck if too many players get in the way.

HostIt sounds like we're waiting for the tech to be perfect before we trust it at all. But isn't some help better than no help? The refs are human, and they make mistakes. Why not use the cameras to at least help them out when they're stuck?

GuestThe league is worried about the flow of the game and the weight of the calls. If they switch to a computer system and it gets a huge playoff goal wrong because a player's sweater blocked the view, it would be a disaster. Right now, they trust the human eye and the video room in Toronto because a person can look at five different angles and use logic to figure out where the puck must be. A computer is very fast, but it's not very good at guessing. If it loses sight of the puck for even a split second, it has to give up. Humans can fill in the blanks, even if it takes a few minutes of looking at replays.

HostSo we're basically stuck with these long breaks in the action while some guy in an office miles away zooms in on a grainy video. It feels like the game is too fast for the tools we have to watch it.

GuestThat's the big tension. The game is getting faster every year. Players are stronger and the equipment is better. We're at a point where the human eye really can't keep up with a puck moving at that speed through a crowd of bodies. The league is actually testing some new setups that use more cameras with higher frame rates, almost like the tech they use for movies. They want to get to a spot where the computer can tell the ref within seconds if the puck went in. But until they can prove it works even when the puck is buried under a pile of three players, they're going to keep the final power in the hands of the people in the video room.

HostThe puck is still a small, dark secret hiding under a mountain of gear and shadows.

GuestThe ice will always be a mirror and the goalie will always be a wall, and for now, those two things are enough to beat the best cameras we have.

HostThat grainy video and the long wait for the ref to point his finger might just be as much a part of the game as the ice itself.