A moment late Sunday afternoon summed up the current state of both the San Francisco 49ers and the Los Angeles Rams: Jared Goff in a heap, the Rams voluntarily regrouping, the 49ers violently forcing an opponent to submit. A wave of 49ers linemen, led by Arik Armstead, sacked Goff on third and long. Strategically, the Rams had no reason not to go for it on fourth down. Practically, there was no point. Coach Sean McVay called off his offense and sent punter Johnny Hekker onto the field.

Two certainties about the NFL are that nothing stays the same for long and nothing is easy. One minute, the Rams were opening as a favorite in the Super Bowl, and every franchise with an opening wanted to copy their head coach. The next, they were surrender-punting their way into a muddle of NFC teams already in a scuffle for playoff contention.

The 49ers’ fortunes have flipped just as radically. An also-ran last season after losing quarterback Jimmy Garoppolo to injury, the 49ers now stand atop the NFC and look every bit the part of burgeoning power. The Rams had started to fall off the mountaintop before Sunday, but the 49ers shoved them and claimed their spot.

The 49ers validated their Monday night shellacking of the Cleveland Browns and cemented themselves as a legitimate Super Bowl contender. They are the NFC’s lone unbeaten team, and their 5-0 record includes a convincing victory over the defending conference champions. Kyle Shanahan has wrested the mantle of trendiest play-calling head coach from McVay.

The way Shanahan wields his running attack is sublime, but the 49ers have thrived on defense. They are simply suffocating opponents. Their years of cratering allowed them to collect a defensive line with four first-round draft picks, three of whom were selected in the top seven: Armstead, DeForest Buckner, Solomon Thomas and rookie Nick Bosa, who on Sunday repeatedly steamrolled Andrew Whitworth, one of the best left tackles in football.

The combination of the 49ers’ marauding defense and Shanahan’s relentless running game has worn down opponents. Do you want to see the effect of great coaching? San Francisco has outscored opponents 86-31 in the second half, and it has not allowed a point in the second half in its past two games.

The 49ers, we know, are legit. But what of the Rams? The long-term smart money is that McVay will figure out their problems, even if they do run deep. Whether he can solve them soon enough in the rough-and-tumble NFC to make the playoffs, let alone defend their conference title, is a different question.

The Rams spent the past two seasons climbing to the top of the NFL and reshaping it in their image. They were both powerhouse and template.

But since they beat the New Orleans Saints in the NFC championship game, McVay’s Rams — the team with the unstoppable offense, cutting-edge roster and newly extended franchise quarterback — are 3-4, including three straight losses. If the playoffs started today, the Rams wouldn’t be in them.

In some ways, the Rams are experiencing standard life in the NFL. The other teams’ coaches live in big houses, too, and once a team finds success, opponents will find ways to attack it. Even great teams can take time to figure themselves out. The Patriots last season were 1-2 with resounding losses to the Jacksonville Jaguars and Detroit Lions. This seems like treacherous territory for the Rams. Really, it’s the inevitable struggle.

But the Rams’ problems cannot be dismissed as a Super Bowl hangover. They’re more concrete than that.

McVay has been forced to reinvent the Rams’ offense on the fly. Last season, they ran almost every play out of the same personnel grouping — one tight end, one running back and three wide receivers. They played offense like Greg Maddux pitched. Everything looked the same until you had to react, and then the result left you confused and defeated.

But several interlocking factors have stymied McVay’s approach. The rushing attack that bludgeoned opponents has been diminished by Todd Gurley’s knee problems. He cannot carry the same load as he did last season, and when he does play, he is not as quick or as powerful.

Goff thrived on play-action passes last season. With Gurley a shell of his best self, it seems evident Gurley propped up Goff, and without him Goff has been exposed. Whether that exposure is temporary or permanent is only the most important question hanging over the Rams, who signed Goff to a four-year, $134 million contract extension just before the season.

Sunday was the ugly nadir of a tough season for Goff. He completed 13 of 24 passes for 78 yards. The 49ers harassed him all day, and the fact he took four sacks is actually testament to how well he got rid of the ball. But there can be no excuse for any quarterback throwing for 3.3 yards per attempt, let alone one installed as a clear franchise caretaker.

Goff’s contract has already had an effect on how much talent the Rams can put around him. They let guard Rodger Saffold walk this offseason in free agency, and his departure has had a more significant impact than many expected. When Gurley sat out, the Rams turned to Malcolm Brown, who is not even a close approximation. The Rams loved third-round pick Darrell Henderson coming out of the draft, but he has contributed essentially nothing.

As Gurley’s health has stifled his production, the rest of the league has finally started to find solutions. By playing a six-man front during the Super Bowl with a fluid combination of zone coverages behind it, the Patriots showed the best way to slow down the Rams. Every team has its own tweaks, but that is the blueprint.

McVay is a gifted play-caller and brilliant offensive mind, not just a coach who came up with a good scheme and has no Plan B. McVay probably will find the right countermoves to how the league has countered him. The Rams have no reason to worry that the league has caught up to McVay, because eventually he will surge back ahead.

In the meantime, though, the NFC is a viper pit, and the next 10 games will be a battle for the Rams to defend their NFC title.

The Rams entered Sunday with rare urgency for a 3-2 team headed into Week 6. The NFC is loaded with viable wild-card contenders, and Seattle’s victory in Cleveland further cemented the NFC West as the NFL’s toughest division. No matter what, the Rams would have left the game in third place in the division. They are now two games behind Seattle and 2½ behind the 49ers. The loss dropped them behind the Minnesota Vikings, Seahawks and Carolina Panthers in the wild-card race, leaving them outside the playoff picture.

With their next three games against the Atlanta Falcons, Cincinnati Bengals and Pittsburgh Steelers, the Rams have an opportunity to right what is haywire with their offense and solidify their shaky status in the playoff hunt.

By Thanksgiving, the Rams’ current struggles may seem like an old story. But they will still have to contend with the 49ers. In the NFL, power can change hands fast. The 49ers have it in the NFC West, and the Rams do not.

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