Maybe I'm reading it wrong, but when it says any player anywhere on the field, it means any lowering of the head... whether it's a QB sneak, or a running back fighting for yards, to a defender trying to make a tackle anywhere that all of this will be 15 yard penalties (letter of the law).
This might be the biggest change ever to the rules, and if so, this would create so much unknown, that almost any player could be a shell of themselves under the new rule. We simply don't know how this will effect players yet.
Basically QB's would be ok because they rarely do sneaks. 95 percent of what they do is outside of that (unless they are a running QB, so someone like Cam Newton could be screwed). This might also decrease the value of Lamar Jackson in the draft. Any NFL team should be asking for in depth meanings BEFORE the draft, because this rule alone could destroy Jackson's future in the NFL. Or it could help. Or both? Weird huh?
Can the specific running back play without lowering his head? In this sense, David Johnson's size, speed, and strength would be an advantage as defenders would have to try to arm tackle him. He runs upright, and that would seem to make these rules a benefit to him.
Goal line and short yardage would be a nightmare for both sides. I can see a lot of flags on both sides making these situations crapshoots one way or another, at least until either the league changes how it is called or players learn to play a different way. Until then, it would be messy. This could also lead to more teams choosing running plays over passing plays that have become more en vogue in short yardage and goal line situations... just to try to trigger a flag.
Of course, they'll have to enforce it to the letter of the law. They may not. So the sky might not be falling. But if they truly enforce it to the letter of the law, this could upset many plans, take millions away from certain players, and get lots of people fired/cut.
Lowering the head is what almost every player does on offense or defense, few hit with the crown which was the 2013 rule. But this, seemingly would at times impact everyone on the field. It could be called on any and every play.
No one knows how these players will play until they have to actually play it this way. Big dollar players should be sweating bullets. There also could be some lower rung players who benefit from the rule. Refs could be very busy. Preseason will be very interesting.
But there was a quote showcasing they want heads up football. So this might entirely be where they are going, and even then, if you try to play heads up, sometimes you are still going to be leading with your head because the circumstances changed quickly. We've seen those called in the past when the defender makes contact to a QB, this could be extended everywhere.
http://profootballtalk.nbcsports.com/2018/03/27/owners-discussing-a-college-style-targeting-rule/
“In our ongoing study of how to make the game better, we just seemed to see more lowering of the head,” Cowboys executive Stephen Jones, who sits on the competition committee, said. “Always we’re looking at ways to improve and make the game safer. And when you look at the plays where the players are dropping their head, we’re doing a good job of catching it after the fact with fines and things of that nature, but probably can do a better job of making the call on the field that hopefully we’ll even emphasize more. Heads-up football.”
So it would seem it's two pronged. One is for better on the fly accountability of the hits that would cause fines and eject them, and in conjunction with another rule, remotely from the league office. Two, in the effort to make tackling heads-up, 15 yard penalties for those lowering their head anywhere on the field to initiate contact.
I don't think they'd flag someone for lowering the head if there is no contact, but I don't see how the ball carrier/defender who both lower their head at the point of contact isn't effected, unless it's not enforced. But why word it 'any player, anywhere on the field' if it isn't?
I also don't see this just as a collision towards the other guy, but also trying to protect the tackler from injuring themselves with a heads down tackle, perhaps even into someones legs. I know a whole lot of concussions have come when a player dives at a ball carrier's legs. Often times because he gets kicked. So this has the possibility to drastically effect the game everywhere. I don't think anyone can rule it out, until the season starts and we see how they call it, unless the NFL specifically lays out certain situations.
Also, which could be really weird, is if both offensive and defensive player lower their head, would that not be offsetting penalties? Thus more flags, more time wasted, longer games, more overall plays which could lead to more injuries backfiring on the owners.
Overall on all of this, we'll see though.