Where does this nonsense about Barron "skating with his head down" come from?
Barron is in a completely normal body position for someone who is a) skating and b) having the puck on his stick. He has not - in any way, shape or form - "lowered his head". His posture didn't change, nor can he do anything about how physics work. It seems like some people really need a course of basic physics to learn how the movement of a body and momentum work. No player who skates hard is in a fully upright position, the body will always lean forward while doing so. Heck, even Trouba, who is skating backwards, is leaning forward a lot. The only time where you are actually fully upgright, is when you are lazily gliding somewhere.
And yes, the onus is on the player who wants to make a hit to make sure that he can actually do so. Again - HE - has to make sure the hit will play out correctly. He can't just waltz around and go for a hit and count on the opponent to put himself in the right situation to be hit in the first place. It is on him to make sure that the player will be in a position where he can land a body check. If a player is standing with his face towards the boards, an opponent can't just run in him from behind and then claim the player should have turned so he could have been hit. No, it is on him to make sure the player is in a position to be hit before he even starts making an attempt to hit. Hits are a means to seperate an opponent from the puck under specific circumstances, not a god given right to enact in any way a player wants. If the circumstances aren't there, then he can't make a hit, simple as that. That's how the rules have always been, no matter how much some people like to pretend otherwise.
And no, players wouldn't just skate with their head down all the time, because a) no one really does that on purpose - and it didn't happen here either - and b) most players know how to land a proper hit or how to stop them in other ways.