The NHL challenge has been another addition to the game which follows the successful model in the NFL, giving another reason for anticipation for fans.
But its reach has not yet been refined.
Years ago, the "horseshoe" blue line allowed Matt Duchene to score a goal for the Avalanche, and yes, that was a blown non-call by the linesmen. It's a tough job, sometimes, especially when it comes to the pinpoint minutiae on what is and isn't an offside or an icing or what not. I am incapable of the job.
Now we have the coach's challenge which is supposed to undo these situations. Perfect. But last night, the Oilers score a goal and it gets called back. Why? An offside call... 40 seconds previous to the play.
The reason the coach's challenge fails here is because in the NFL, you have one play, a stoppage, another play, a stoppage. The format makes it a lot easier to appraise each individual play because the game is broken down into plays. However, the NHL has a different type of game where plays flow into each other, so once one play ends, another begins. We only call them "plays", but they're not the same as football plays, so it would be more apt to assign them a different name, like an "event".
The event that preceded the goal had fallen out of relevancy at the part of the game it affected. After about ten seconds after breaking a zone, whether the play was or wasn't offside doesn't matter anymore. In order for the Coach's Challenge to work like the NFL, the coach would need a whistle or a flag to throw at the official to blow the play dead.
This would be a nightmare, because if it's a legit play, it would mean an unnecessary stoppage to the game, which would be an abused play by a coach. (Coaches will abuse all systems because their job is to win hockey games: if they weren't getting paid, we might expect some semblance of honour).
The Coach's Challenge is perfectly legitimate for an offside call if it occurred off a rush, but in any case where zone pressure is already established and a goal is scored, it's a farce. "Should there have been zone pressure?" It doesn't matter. The goal wasn't scored as the result of the offside, but as the result of a perfectly legitimate play that occurred after this may or may not have affected the game.
The NHL is a butterfly-effect game, which I think is difficult to remember at times: that goal that was called off in the first period is far less likely to affect the outcome of the game than a goal called off near the end of the third period. This is why you see referees tend to back off near the end of the game, so as to not change the game on a single call (like a Gretzky high stick). A play that directly results in the event of an offside is of course an immediate result of the offside, but the more events happen after the offside, the less the offside matters to the overall play.
The Coach's Challenge should then immediately be changed to only question an event that directly precedes a goal (a grace period of about nine seconds). If the missed offside occurred more than nine seconds before the goal, it cannot be challenged.
After this change, they'll need to continue to refine the Coach's Challenge so that it works better with the NHL model of play, where you have a continuity of events rather than a series of play stoppages. Maybe I imagine a big red button that a coach can push when there's an offside behind the bench, and as soon as the missed infraction happens, the coach runs over and jams it with his best ruthless-war-machine face, and guys overhead look at the play in question while the play goes on and notify the linesmen to blow the whistle if there's a clear infraction, but I doubt they'll ever institute anything with much intuition in the NHL.
So it's simple: if it's 10 seconds ago, it doesn't matter anymore.