2021 NFL season: One challenge each undefeated team must overcome

Carolina must: Prove the defense really is one of the NFL's best.

In 2020, the Panthers' defense ranked 18th overall, 18th in points allowed, 18th against the pass and 20th against the run. To say they've improved significantly in 2021 is an understatement; two games in, Carolina ranks first in all four categories. The Panthers have made an even more dramatic jump in third-down defense, which coach Matt Rhule told me last week was a real focus, leaping from 31st in 2020 to first this year.

It is entirely plausible that this unit has turned a corner in Year 2 under Rhule and defensive coordinator Phil Snow, with players like free-agent addition Haason Reddick, rising youngster Brian Burns and veteran Shaq Thompson really dialed in thus far. But we won't know for sure that the D can help keep Carolina in the upper echelons of the NFL until we see it happen. The Cowboys in Week 4 will offer a good early test.

Las Vegas must: Avoid another late-season collapse.

One AFC head coach told me recently that he thinks the Raiders are one of the best teams in the NFL right now. The key for Las Vegas is to avoid falling prey to the late-season collapses that have doomed previous fast starts in the second Jon Gruden era. In 2019, a 6-4 start was ruined by a 1-5 finish, and last season's 6-3 record was waylaid by a 2-5 mark in the stretch run. Gruden tends to work his guys really hard early on, and while that approach can help build momentum for a playoff push, the risk is that players might wear out. Derek Carr, who is currently playing very well, also tends to slow down later in the year, with his passer rating dropping from 96.5 in September and 99.4 in October to 86.6 by December. Whether Gruden adjusts his approach or Las Vegas focuses on shoring up depth at the bottom of the roster, the team will need to figure out a way to stave off the winter doldrums.

Tampa Bay must: Get more out of the run game.

Tom Brady is one of the most amazing people I've ever met in my life, and his blazing-hot start (nine touchdowns in two games) leaves little to criticize about the Bucs. At this point, it would be foolish not to assume he'll be playing as well in January as he is now, even after going through a 17-game season at age 44. Still, it wouldn't hurt to make things as easy as possible on him, and getting more production out of the ground game -- Tampa ranks 30th in rushing yards, 29th in rushing TDs and 23rd in yards per carry this season -- would surely help. In 2020, Ronald Jones averaged 69.9 rushing yards per game (5.1 per carry) in the regular season, while Leonard Fournette put up 75 per game (4.7 per carry) in the playoffs. This season, though, those marks have dropped precipitously (42 per game and 4.2 per carry for Fournette; 20.5 per game and 4.1 per carry for Jones). I don't want to read too much into such a small sample size, but giving Brady a more robust rushing attack to lean on would only ease the path back to the postseason.

Denver must: Stand up to stronger competition.

The Broncos have eaten up the likes of the Giants and Jaguars so far, with perhaps the most surprising aspect of their strong start being the play of Teddy Bridgewater and the offense. Bridgewater entered the season with career averages of 260.3 yards per game and 7.3 yards per pass, having thrown 53 total touchdown passes against 36 interceptions. All of that added up to an 89.5 passer rating. He has soared past those marks in 2021, tallying nearly 300 yards per game, with a 4:0 TD-to-INT ratio, 8.5 yards per pass and a sky-high passer rating of 120.7. When the schedule starts to heat up (vs. Baltimore in Week 4, at Pittsburgh in Week 5, vs. Las Vegas in Week 6, at Cleveland in Week 7), the Broncos would be well-served if Bridgewater and the offense could continue to shine and help shoulder some of the load that will be carried by Vic Fangio's defense.

Los Angeles must: Help Matthew Stafford hit new heights.

Like the Buccaneers, the Rams appear to be a well-rounded machine. New quarterback Matthew Stafford has thrived. Cooper Kupp is solidifying his status as a bona fide No. 1 receiver. The defense is stacked. As with Tampa, it was difficult to find weaknesses or challenges for this team. There is, however, one personal hurdle Stafford will have to clear in the near future: vanquishing high-caliber opponents. Since he entered the NFL in 2009, Stafford has compiled a career mark of 8-65 against teams that finished the season with a winning record, with a passer rating of 83.5. That has a lot to do with the fact that he was on bad Lions teams for most of that time, of course. And I fully expect him to mow down defenses for the duration of the season, now that he's surrounded by a more capable supporting cast. But the true test of that premise will be how he performs against the other elite teams in the NFL. Sunday's showdown with the Bucs will provide a nice early measuring stick. 

Arizona must: Slay the NFC West dragon.

The Cardinals are 2-0 for the second time since Kliff Kingsbury became head coach in 2019. They upgraded a roster that was strong enough to go 8-8 in 2020, and it's translated to success so far. Kyler Murray is also off to the hottest start of his young career, posting a 7:3 TD-to-INT ratio and a passer rating of 121.5, obliterating his marks in Weeks 1-2 in 2019 (2:1, 81.7) and 2020 (2:2, 83.1). Looming over all this positivity: the NFC West portion of Arizona's schedule. Kingsbury has a 3-9 record against the other three teams in the division, including three second-half losses last season (one each to the Seahawks, Niners and Rams) that helped torpedo the Cardinals' playoff chances. It's going to be tough to keep the good times going in the desert if Arizona isn't able to reverse this trend. Week 4's trip to play the Rams in Los Angeles offers the first chance to make progress in this area.

San Francisco must: Stay healthy.

Most predictions of a strong San Francisco season rested on the assumption that the 49ers' injury luck had to improve after health issues derailed their 2020 campaign. Unfortunately for San Francisco, several key players have been sidelined already, whether for the long term (cornerback Jason Verrett and running back Raheem Mostert, who were lost for the season) or short (three running backs left early in Week 2). This team was able to win in the first portion of last season, too, but ultimately collapsed. If they are to escape the same fate in 2021, the Niners will have to keep the rest of their core group on the field. It would also help to shore up running back depth with players who fit Kyle Shanahan's one-cut scheme.