Ron Parker and Chris Jones pull Tom Brady down in the end zone after he scored his fourth-quarter touchdown. (Greg M. Cooper/USA Today)

The NFL’s rules on roughing the passer, enacted largely to protect guys such as Tom Brady, came into play at a crucial moment in the “Sunday Night Football” game between the New England Patriots and Kansas City Chiefs, with the beneficiary being . . . Tom Brady.

With a little over five minutes left in the game and the Chiefs leading, 33-30, Brady and the Patriots had driven to the Kansas City 4-yard line. It looked as if Kansas City then snuffed the drive when Brady dropped back to around the 12. Breeland Speaks enveloped him in what was certain to be a sack until it wasn’t, because Speaks inexplicably released his grasp. That was all Brady needed and he took off, rambling like a 41-year old dad into the end zone.

What, exactly, was Speaks thinking when he let go of Brady? The rule book. The rookie linebacker said, “I thought the ball was gone,” and that he was trying to avoid a costly penalty.

“It was definitely on my mind,” Speaks said of the rule (via NFL Network). “It sucks. You’re supposed to finish plays like that.”

This has been the season of roughing the passer, with uneven enforcement making the rules the prime topic of conversation every week. The Packers' Clay Matthews was flagged for quarterback hits in each of the first three games. The Dolphins' William Hayes said he tore his anterior cruciate ligament trying to ease up on a play. Steelers Coach Mike Tomlin was fined by the league after questioning enforcement last week, saying, “Some of the other stuff, man, is a joke. We gotta get better as a National Football League. Man, these penalties are costing people games and jobs. We gotta get ‘em correct. So I’m [angry] about it, to be quite honest with you.” The Texans' J.J. Watt also was angry when his brother, T.J., of the Steelers, was fined for a quarterback hit last week. Even quarterbacks such as Ben Roethlisberger and Aaron Rodgers, guys the rule was designed to protect, have questioned its application.

The NFL competition committee stepped in to try to clarify the way in which the rule was being officiated, The Post’s Mark Maske wrote last week, and to shift enforcement more in line with the committee’s expectations. Roughing was called 34 times in the first three weeks. Then, after the competition committee met by conference call, there were only five such calls in Week 4. But the number crept back up to 11 in Week 5, and players have spoken about how conscious they are of it.

“I think they just sometimes lack common sense,” Eagles safety Malcolm Jenkins said last week. “I get it. We want to protect quarterbacks, and I completely understand that. They’re the lifeblood to our game. But it’s really hard to do your job, and it’s having an effect on some games.”

Speaks also knew where he was playing, suggesting that Brady was going to get the benefit of the doubt from officials. “Especially in New England. We’re in New England,” he said (via the Kansas City Star). “Tom’s going to get the call.”

The play ended up being somewhat irrelevant, other than the important experience it gave Speaks and the conversation it generated, because the Chiefs were called for defensive holding, which would have given the Patriots an automatic first down. But Speaks, who earlier in the game forced a Brady fumble, learned a lesson as the Patriots outscored the Chiefs, 16-14, in the fourth quarter and went on to win, 43-40, in the game’s waning seconds.

What was the rookie’s takeaway? “I gotta finish the play next time.”