According to NFL official Pete Morelli, who explained the league's rule changes to a group of Twin Cities media on Thursday, Barr's hit would fall under a point of emphasis the NFL has instituted for 2018. It would be a 15-yard penalty for roughing the passer.
Rule 12 in the NFL's 2018 rulebook details player conduct. Under Article 9, which explains the rules around roughing the passer, the manner in which a quarterback in a defenseless position (which is just after he has completed throwing a pass) is tackled is the point of emphasis.
The rule states the following:
"A rushing defender is prohibited from committing such intimidating and punishing acts as 'stuffing' a passer into the ground or unnecessarily wrestling or driving him down after the passer has thrown the ball, even if the rusher makes his initial contact with the passer within the one-step limitation provided for in (a) above. When tackling a passer who is in a defenseless posture (e.g., during or just after throwing a pass), a defensive player must not unnecessarily or violently throw him down or land on top of him with all or most of the defender's weight. Instead, the defensive player must strive to wrap up the passer with the defensive player's arms and not land on the passer with all or most of his body weight."
According to Morelli, everything boils down to whether a defender uses his full body weight to bring down a quarterback any time he is in a defenseless position.
"Players will have to kind of roll to the side when they make that tackle instead of plopping down on him [the quarterback]," Morelli said. "The Aaron Rodgers [tackle] would be a foul this year. As long as he's out of the pocket, established and all that. But if he's running, that's not the same."
On the play in question, Rodgers rolled out of the pocket to his right and launched a pass. Barr took the two steps required before wrapping the quarterback up by the waist and tackling him.
Upon being tackled, Rodgers braced himself with his right (throwing) arm as he hit the turf. Barr brought Rodgers to the ground and rolled off the quarterback's left shoulder within seconds of completing the tackle. Barr was not penalized.
The rule, according to Morelli, applies to a quarterback whenever he's in a defenseless position, which could be in the pocket or whether he runs and sets up again outside of the pocket.
"If you roll out and get set up, you're still a passer," Morelli said. "But if you're rolling out and throwing and a guy's chasing you and tackles you, you're not defenseless. They get two steps and they can tackle you. Becoming defenseless is setting up again outside the pocket."
Barr said later Thursday that it will be "very difficult" for defenders to adjust and make a split decision while in motion to prevent drawing a penalty.
"You're playing fast, trying to make a play on the ball. It's going to be tough. It'll be interesting to see how that's officiated and how it's called this year. This year there's going to be some debate from the players, from the coaches, from the officials as to who's right, who's wrong, but we've got to try our best as players to play within the rules," he said.
Barr, however, said it's not worth complaining about rule changes.
"It is what it is. You can complain about it all you want, but it's not going to change unless they change it, right? It's your duty as a player to continue to play by the rules and not penalize and hurt the team. That's what we're going to try and do," he said.