At 13:12 of the third period in the Predators/Penguins game, Nashville requested a Coach's Challenge to review whether Matt Cullen was offside prior to Pittsburgh's goal.
After NHL Hockey Operations staff and the Linesmen reviewed all available replays, it was determined that Cullen preceded the puck into the attacking zone, causing an offside.
Coach's Challenge: NSH @ PIT - 13:12 of the Third Period
Original call is overturned, no goal Pittsburgh