How? Was he supposed to crouch down? The guy is like 6'8" and his arm was down. This is going to happen again because of his sheer size.
Needs to recognize the vulnerability and let up. Bastian was somewhat engaging with another Ranger which makes it even worse. If he lets up and still hits the head ,the league would be much more forgiving. The onus, whether we like it or not, is on the hitter. This isn't 1994 anymore. Trouba is great at hitting guys when they're standing tall, and crushing their chest or shoulder with hits. The key is his initial point of impact is not the head. Sometimes the head does get hit by trouba, but that's after he hits the should or chest and drives through. It's much more difficult to line guys up like he does. Or crush someone into the boards when they're facing you. You just can't destroy the head nearly full speed anymore and expect the league to shrug their shoulders because the guy getting hit was oblivious with his head down.
Just adding that unless you're living under a rock you KNOW there's lots of talk about head shots in sports, and lawsuits for early death/dementia. 'That's sports lol' works until you're getting class actioned by former players, getting terrible PR, and losing youth participation in the sport. The NHL needs to show they don't tolerate headshots so they can turn to the attackers and show how they severely penalize it and are doing their best to remove it from the game.
After the 04 lockout the NHL went full force on removing obstruction and if defenders so much as moved an inch to the side to impeded the attacker it was called interference. The end results was forwards FLYING through the NZ and blue line on dump ins, unimpeded, and when the weak side defender met them at the boards it was limbs and heads flying into the boards at top speed. The NHL quickly realized they need to slow down the players on dump ins and began to allow more movement out of the defenders lane to impeded the attacker, so even if the attacker got by, it was a more lateral approach with less end to end speed.