It was one of those moments when you felt a subtle shift in the undercurrent.

Two minutes gone in the second quarter, the Eagles up six, the Patriots with a first down on their 36-yard-line. With his pocket collapsing, Tom Brady stepped up and saw a wide open Brandin Cooks 21 yards down field. The diminutive receiver squared his body and attempted to make an open-field move on a defender 3 yards in front. But just as he accelerated into his first step, a streak of midnight green flashed into his left-hand periphery. The resulting hit by Malcolm Jenkins left Cooks crumpled in a motionless heap on the Eagles' 40-yard line and the Patriots without their best outside-the-numbers threat for the rest of the game.

>>READ MORE: Relive the Eagles' Super Bowl win

Six months after the Eagles celebrated their stunning victory in Super Bowl LII, Jenkins' second-quarter encounter with Cooks has emerged as a case study in the uncertainty surrounding a hotly debated change to its rule regarding contact with the helmet. On Saturday, it was central topic of an at-times heated discussion between Eagles defenders and NFL officials during a briefing on the new rules that the officiating crew delivered to the team in the NovaCare Complex auditorium. Ostensibly, the 45-minute video presentation and subsequent question-and-answer session was held to eliminate any uncertainty surrounding the new rules. Yet, by the end of the briefing, the confusion had only thickened, its nexus arriving when, according to multiple Eagles players, two different officials offered two different opinions on the legality of Jenkins' hit under the new rules.

"We were trying to ask questions to get a better understanding, and yet they couldn't really give us an answer," linebacker Nigel Bradham said.

The only thing that everybody can agree upon is that the NFL's intent is clear. Understanding it only requires one look at the physical bylaw proposal voted on by the NFL's 32 clubs this offseason. No longer does Rule 12, Section 2, Article 8, feature the heading "INITIATING CONTACT WITH THE CROWN OF THE HELMET" followed by a detailed 89-word summation of the forbidden act. In its place are the words "USE OF HELMET" and a single sentence: "It is a foul if a player lowers his head to initiate and make contact with his helmet against an opponent."

"Obviously, there are certain things that they are trying to get out of the game that we can all agree upon are plays that have any effect on the play," defensive end Chris Long said. "Somebody that is just recklessly leading with their head. We can all agree on that."

But, he continued, "There are some nuances that I don't understand yet."

"Nuance" is not the first word that comes to mind when you watch a replay of Jenkins' hit on Cooks. In fact, it might have been the play the NFL would have picked if it had charged its competition committee with the mandate, "Eliminate this." Start with the end result: a player's head violently twisting on impact, his body going limp, the national TV cameras showing him walking into the locker room as play continues. Continue with the means: Jenkins' helmet is lowered, his face mask angled toward the ground, his arms beneath the plane of his shoulders. He is a human missile, the epitome of maximum destruction from an open-field ball carrier's point of view. Mind you, that's not his fault. Maximum destruction is what he is paid to inflict, and for good reason.

Yet if the goal is to make the game safer, then eliminating this kind of encounter is the best way to achieve that. Even under the old rules, which focused specifically on "forcible contact" with the crown of the helmet, the play could have been ruled a penalty, given the way the top of Jenkins' helmet appeared to strike in the vicinity of Cooks' earhole. For a rule to be improved, it would need to eliminate any of that gray area, particularly given the stakes involved. In this case, we had a potentially decisive moment in the decisive game of the NFL's season. Had the hit drawn a penalty, the Patriots would have had a first down on the Eagles' 22-yard line, potentially leading to (at minimum) a field goal instead of a failed fourth-down attempt from the 35.

Which leads to the question: What good is a rule that does not offer a definitive judgment in that sort of situation?

"It's confusing," Long said. "One thing I will say about the competition committee and changing the rules, there is not one active player who is involved in the process when it comes to changing a rule on the field of play … When they change rules like that, they should get input from people who can say, 'This is why what you are proposing is really difficult.'"

"Listen, basically, the general rule is, just don't drop your head," Eagles head coach Doug Peterson said. "As a ball carrier, as a defender. All things that we were taught as young players in football: keep your head up, see what you hit."

Yet, what is simple in theory is often more complex in practice, as evidenced by the questions that still remain.

>>PRACTICE OBSERVATIONS: Day 1 | Day 2 | Day 3 | Day 4