You won’t believe why Trevor Zegras was sent to the penalty box!

The Philadelphia Flyers and Boston Bruins were grinding through a fairly routine preseason contest on Thursday night, but midway through the second period, the game took a turn nobody expected when star forward Trevor Zegras was whistled for one of the most unusual penalties you will ever see.

Zegras was called for "improper wearing of equipment." In real time, nobody in the building or watching at home seemed to have any idea what had just happened.

As it turned out, the infraction was a tucked jersey. That's it. Zegras had his sweater tucked in, and the officials decided it warranted a trip to the penalty box.

It has been explained that the league has signaled that it plans to crack down on equipment violations this season. That includes neck guards, visors, helmets during warmup, and yes, jerseys. Players are expected to have their jerseys untucked at the start of every shift, though the league reportedly will not penalize a jersey that rides up naturally during play.

Insiders like Elliotte Friedman also noted that the enforcement protocol involves a warning first, followed by a two-minute minor for a second offense. A third violation would reportedly result in a misconduct. Based on that sequence, Zegras was apparently warned earlier in the game before the penalty was assessed, though any such warning went completely unnoticed by viewers.

Both Zegras and teammate Travis Konecny argued the call with the officials, but their protests went nowhere.

The penalty came at a particularly bad time for Philadelphia. Shortly after Zegras sat down, Jett Luchanko was called for hooking, putting the Flyers in a 5-on-3 hole. The team managed to kill off both penalties and survive the sequence.

It was the Flyers' first individual penalty of the night. Their only prior infraction had been a too many men call served by Matvei Michkov, who had also scored the game's opening goal.

Philadelphia being the first team to get burned by this particular enforcement push felt almost inevitable to long-time Flyers observers. The franchise has a knack for being the guinea pig when the NHL decides to make a point about a rule.

It’s so funny that now players can dress how they like when coming to games but the jersey tuck penalty stands as an early warning to every player across the league. If the officials are willing to call it in a meaningless September exhibition, there is every reason to believe they will call it when the games count for real in October.