The Cleveland Browns were livid Sunday afternoon, for all the wrong reasons, when referee Shawn Hochuli picked up a flag for an illegal hit to the head of quarterback Baker Mayfield. Although Mayfield appeared to be giving himself up in a slide, Hochuli ruled that he was in fact still a runner and did not have protection against such hits.

"That was different from what I know," Browns coach Hue Jackson said, while receiver Jarvis Landry remarked, "Every other quarterback gets that call."

But both the postgame debate and Hochuli's explanation failed to address an entirely different but no less obvious foul. Whether or not Mayfield deserved quarterback protection on the play, Tampa Bay Buccaneers defensive back Jordan Whitehead had clearly, without question, violated the new NFL rule prohibiting players from lowering their helmets to initiate contact on an opponent. In real time, at least, no one seemed to notice.

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Replays showed Whitehead boring the top of his helmet into the side of Mayfield's head -- with a running start, no less -- and utilizing the linear posture that NFL research has shown increases the likelihood of head and neck injuries. Whitehead's hit was so flagrant, and his ability to avoid it so clear, that he might have fit the league's stated criteria for ejection. The foul went unmentioned by the Browns, Hochuli and the broadcast announcing crew, in the process cementing the disappearance of the helmet rule from our national consciousness.

The no-call isn't entirely unexpected, though, given how the NFL is implementing the helmet rule. In a highly irregular but understandable approach, the NFL has intentionally delayed enforcement of a major rule, largely because it recognized that immediate and full application would have required an unrealistic adjustment for players.

Instead, the league has presented a soft rollout, penalizing players only occasionally to avoid flag-filled games but following up with more-than-occasional fines and dozens of warning letters to players and teams. The warning letters spell out violations that went uncalled, with video, and advise that similar hits will be penalized in the future.

Helmet rule enforcement through Week 6 Total Offense Defense Special teams Called on field 7 0 6 1 Fines 11 1 9 1 Warnings 65 15 43 7

"In the offseason it's an easy thing to discuss and an easy thing to put tape to," said Rich McKay, chairman of the NFL competition committee, during a meeting with reporters last week. "But when you actually practice it, it's a totally different thing. Players are still trying to adjust because it's not the natural way that they have played the game over the last five years or in college. …

"The one thing we did is go through the tape and say [to officials], 'If you don't see it end to end and don't see all three elements of it, then remember we can fine it on Monday and we can get the conduct corrected.'"

Through the first six weeks of the season, officials threw just seven flags for use of helmet fouls but issued 11 fines and sent 65 warning letters. (Through Sunday night's game, there has been only one additional flag. Week 7 fines and warning letters, if any, will go out later this week.) Those numbers suggest the league has allowed about 90 percent of violations to go unaddressed during games.

It is not uncommon for the league to fine players for fouls that were not penalized by on-field officials. Nor is it unusual for it to send warning letters. But the size of the differential -- the number of warning letters and fines compared with the number of flags -- is unprecedented in recent league history, according to several people I spoke with who have institutional knowledge of the way the league approaches rule enforcement.

The simple explanation is the league has never attempted to eliminate a behavior that had become so ingrained and common in the game.

When owners unexpectedly adopted the helmet rule last spring, responding to league research that showed the dangers of a head-down and linear position, officials in the league's football operations department inspected tape of the 2017 season. They estimated the rule would add between 4-5 additional penalties per game if strictly enforced. With all else being equal, the league would see a 31 percent increase in flags over the course of the season. And at 15 yards a pop, total penalty yardage would jump 64 percent.

No one wanted that. More importantly, a two-day football summit in May made it clear that players would need time to learn the techniques and develop the muscle memory that would break the habit of lowering their heads ahead of contact.

"There are certain things that are incidental contact and just part of this sport," Troy Vincent, the NFL's executive vice president of football operations, said at the time. "There are certain things you just have to live with and be OK with. And then there is the part of our role and responsibility. What do we want to coach out and then the players have to adjust to? Some of these things are more long term.

"To think that an individual player will make some of the adjustments between May 1 and the start of the season, when this is what I have done all of my life? That's unrealistic. That's truly unrealistic."

The first two weeks of the preseason offered a preview of what could be expected by relatively strict enforcement. Officials threw 51 flags in the first 33 preseason games before the competition committee clarified that it never wanted incidental or inadvertent contact to be called. For 2018, at least, the league wants flags thrown only when an official spots, from start to finish, obvious and intentional instances of a player lowering his helmet and using it for initial and forcible contact.

Even with that edict, we've seen some obvious and high-profile plays when the helmet rule could have been called. It seems likely that Whitehead will receive a fine or a warning letter for his hit on Mayfield. Kansas City Chiefs running back Kareem Hunt was fined $26,739 for a contact in Week 4 that he was not penalized for. New England Patriots running back Sony Michel wasn't penalized for contact that gave Indianapolis Colts defensive back Clayton Geathers a concussion in Week 5, but senior vice president Al Riveron later used the play in a public video to demonstrate that it was in fact a foul.

This approach makes sense for the purposes of game flow and fairness, but it also raises some fair questions. Why have a rule book if some of its requirements aren't enforced? If administration is selective, does that increase the chance it will favor or hurt particular teams? And if most of the violations have been addressed only in warning letters, should that call into question whether this whole episode has been for show? Has the NFL in essence written a check that it can't cash, simply to appear concerned about the head and neck health of players?

I don't think that's the case. The NFL already has provided too much public information about the root of the rule and its enforcement to carry out an effective ruse. At the end of the season and beyond, we'll know via relatively objective numbers whether contact decreased between lowered helmets. The real question is whether the NFL can achieve its goals via warning letters or fines, or if the day will come that we see multiple flags per game, rather than perhaps one for all games of the week combined, to change the behavior.

McKay said last week that "we like where the data is starting to take us with helmet impacts" but that full answers will be more apparent at the end of the season when the league compiles and analyzes the data. It typically makes public its annual concussion numbers. In the meantime, Vincent did not rule out stricter enforcement as the weeks go on.

"We hope that [through] the education process, that there is greater accountability, so we don’t have to fine," he said. "Players have to get the shoulder in and head out. The helmet is a piece of protective equipment. It's not being used to harm your opponent. We hope we don't have to get there but it's a progression."

We knew from the beginning that the NFL was attempting a sizable change with the helmet rule. What we didn't realize was that the league would follow an alternative path to get there. The approach is unusual in its scope and should be employed sparingly with future rule changes, but in this case seems preferable to a massive spike in penalties. Will it work? We'll find out soon enough.