With the Lightning facing the Avalanche in the Stanley Cup Finals, both teams have to utilize the challenge system to their advantage. How many challenges in NHL?
The coaches challenge was introduced at the beginning of the 2015-16 season. Initially, it was limited to just a few challenges per game, as a coach would have to use a timeout to challenge a goal.
The only calls that can be challenged are offsides and goalie interference.
In the first period of Game 3, the Lightning challenged a non-call by the officials, assuming that the Avalanche were offsides for their first goal of the game. They were right, and therefore were not penalized.
How many challenges in NHL
Since the start of the 2019-20 season, teams can challenge an unlimited number of times. However, if they are wrong, they are penalized.
NHL offside rule
Per a quick google search, Rookie Road explains offsides better than I ever could.
“In hockey, the offside rule prohibits players from entering the offensive zone before the puck has crossed over the offensive blue line. If a player without the puck crosses the blue line before the puck, the play will be whistled dead for an offside infraction.”
And there you have it.