Super Bowl 50 was a game Broncos fans will want to remember forever and one Panthers fans have been trying to forget for months. Instead of leaving that dominant Denver performance in the past, though, it seems Carolina and Denver are still reliving that fateful night in Santa Clara in the first month of the 2016 season.

While the Broncos only narrowly prevailed over Carolina during their rematch in the opening game of the regular season, they have gone 4-0 while starting over at quarterback and are on the short list for football's best team.

The Panthers, meanwhile, are in a free fall. They were ripped apart on Sunday by Matt Ryan and Julio Jones, who hit 501 passing yards and 300 receiving yards, respectively, in a 48-33 romp that saw Cam Newton leave after suffering a bizarre (and avoidable) concussion. At 1-3 and with Atlanta possessing the tiebreaker between the two teams, Carolina is 2.5 games back in the NFC South after four weeks. ESPN's Football Power Index gives the Panthers just a 37.2 percent chance of making the postseason.

The 2015 underlying numbers suggested each of these teams would decline a bit in 2016, and they both made controversial decisions to move on from would-be contributors during the offseason and go with unproven talent at a critical position. So why have the Broncos flourished while the Panthers have struggled? And will it continue to go on this way?

Let's take a closer look at Denver and Carolina to see what's up with the defending conference champions.

Von Trap

You know the old adage: If it ain't broke, don't fix it, right? The Broncos obviously weren't broken last year, and despite their roster turnover, they brought back enough of their core talent to stick with the same principles which led them to their Super Bowl win a year ago. In fact, the Broncos are doing a better job of doing the things they did well in 2015 here in 2016. They're a more Broncos version of the Broncos.

Almost across the board, Gary Kubiak's team is playing better than it did last season. The one exception is run defense, which was fourth in DVOA last year and all the way down in 30th this season before Sunday's win over the Buccaneers. Denver did well enough against the run there to ensure that its ranking will improve, but it's still a glaring weakness for a team that is pretty good or better at just about everything else.

The improvements start, strangely, at quarterback:

1. Trevor Siemian and Paxton Lynch are an upgrade over Peyton Manning and Brock Osweiler. It would be wrong to pretend that Siemian has looked like a superstar in the way that Carson Wentz and Dak Prescott have performed during their stunning debuts, but Siemian has been perfectly acceptable, which is a step up from what the Broncos got from their quarterbacks last year. Last year, Manning and Osweiler produced a combined QBR of 52.1, which was 25th in the league. Their 76.3 passer rating was 31st in the NFL. In the first quarter of 2016, Siemian and Lynch, who replaced an injured Siemian on Sunday, have combined for a QBR of 67.8 and a passer rating of 98.6. Those figures are 12th and 10th in the league this season, respectively.

So far this year Trevor Siemian is 15th in QBR, ahead of Houston's Brock Osweiler. Jonathan Dyer/USA TODAY Sports

While Siemian has had trouble with some of his decision-making and thrown his passes just 6.7 yards in the air, which is 28th among qualifying quarterbacks, he and Lynch have managed to protect the football. Last year, Peyton & Co. turned the ball over on 15.1 percent of their offensive possessions, which was the sixth-worst rate in the league. This season, through four games, Kubiak's offense has given it up on 11.1 percent of its drives, which is just below league average (12.2 percent) and good for 16th. Simply average is a significant upgrade for the Broncos, and the improvement in giveaways has helped them in another key way:

2. The offense has made things easier for the Denver defense. Quietly, what made the 2015 season even more impressive for the Broncos' defense is how often it stepped up with terrible field position. The average Broncos defensive series last season started with 70.5 yards to go for a touchdown, meaning the D took the field right around the opposition's 30-yard line. That was the third-worst average starting field position for a defense in the NFL last year, and the short fields made it more difficult for the Broncos to come up with stops.

With fewer turnovers, naturally, the Broncos have had more breathing room to work with on defense. Their typical defensive series in 2016 has begun with 73.6 yards to go for a touchdown, starting the Broncos off closer to the opposition's 26-yard line. That would be the 10th-best average field position in football for defenses this year. It might not seem like much, but those 3 yards add up over the course of a 180-possession season. Denver was also stuck facing a league-high 195 meaningful drives last year per Football Outsiders, which was the equivalent of playing a 17th regular-season game. This year, they're on pace to defend 172 meaningful possessions, which is just below league average. The extra rest can only help Denver and its defenders.

3. The pass defense has somehow gotten scarier. Denver posted the league's best pass defense last year, hitting a staggering minus-28 percent in DVOA when the Panthers were the only other team in football below minus-10 percent. They were at minus-22.0 percent before the Bucs game and should improve, given that Jameis Winston was the worst quarterback in the league this week per adjusted net yards per attempt (ANY/A), calculated by Chase Stuart of Football Perspective and FiveThirtyEight.

The Denver pass rush was also atop the leaderboard a year ago and has still managed to improve. The Broncos led the NFL in sack rate (8.1 percent) and pressure rate (34.7 percent) last season. Despite getting just 45 snaps from DeMarcus Ware so far this season, they haven't missed a beat, and Von Miller is the current NFL leader in sacks. While the Vikings have the league's highest sack rate, Denver has taken down opposing passers on 10.4 percent of their dropbacks, nearly a 29 percent improvement on its sack rate from a year ago. The Broncos are pressuring opposing passers 38.4 percent of the time when nobody else is above 32.3 percent. Even the Vikings can't top that.

Von Miller leads the NFL with 5.5 sacks through four weeks. Dustin Bradford/Getty Images

To put it in context, the Broncos were seventh in the league last season in terms of contacting the quarterback, which they did on 13.9 percent of dropbacks. This year, the Broncos are making contact on 25 percent of pass plays. Nobody else is above 17.5 percent. They're lapping the field there. Denver has the best pass rush in football right now, and when teams get passes off, Aqib Talib & Co. are lying in wait in trap coverage, waiting to snatch throws out of the air. They're picking off 3.3 percent of opposing passes, the fifth-best rate in the league.

4. The injuries they've suffered have been in places of relative strength. The Broncos are a pretty deep team, but they've been lucky in that their injuries have hit places they were prepared to handle. Ware's absence might have crippled some teams, but the Broncos were ready with 2015 first-rounder Shane Ray in reserve. Ray has three sacks and five quarterback hits in two starts. Siemian reportedly suffered a sprained AC joint in his non-throwing shoulder Sunday, which caused him to miss the second half, but Lynch, the team's 2016 first-rounder, dropped into a shotgun-heavy attack and kept the Broncos out of trouble.

5. The schedule has been relatively easy. One relatively simple way to measure strength of schedule is to look at what a team's opponents have done in the games that didn't involve the team in question. In other words, what have the teams who have played the Broncos done when they weren't lining up against Denver? The answer is, well, not much. The Panthers, Buccaneers, Bengals and Colts have gone a combined 5-7 while being outscored by 34 points. Compare that to Carolina ...

Carolina Blues

1. The schedule has been extremely difficult. It's not the biggest problem the Panthers are facing, but since I just mentioned it for the Broncos, let's start here. By the same measure above, the teams Carolina has faced this season have gone a combined 8-3 in games not involving the Panthers this year, outscoring their opposition by 85 points. Carolina's three losses have come against the Broncos, Vikings and Falcons, who each lead their respective divisions. For what it's worth, their next two games before a Week 7 bye are against the Buccaneers and Saints.

2. Cam Newton has been way less productive. I don't think Newton has been the biggest problem for the Panthers, but his drop-off has been noticeable. The reigning MVP ranks just 25th in opponent-adjusted QBR this season at 51.3; last year, he was 12th in the same category. Some of that owes to the fact that he has been pressured more frequently, which is obvious in watching Cam play. In 2015, Newton was sacked on 5.9 percent of his dropbacks and pressured 27.0 percent of the time, which ranked 19th and 16th in the league, respectively.

Cam Newton left Sunday's game after taking an unnecessary hit on a two-point conversion run. AP Photo/John Bazemore

Through the first four games this year, Newton has been sacked on 7.6 percent of his dropbacks and hit 28.7 percent of the time, which has him 30th and 27th in those same categories. It was easy to chalk those pressures up to the dominant defenses of Denver and Minnesota, but the lowly pass rush of the Falcons hit Newton and Derek Anderson eight times on 49 dropbacks Sunday. They pressured Newton on 30.8 percent of his dropbacks after posting a pressure rate of just 19.8 percent through the first three weeks, which was fifth worst in the NFL.

Those hits have also seemed to cause more injuries. Newton was beaten up during the opener against the Broncos, infamously and inexplicably avoiding the league's concussion protocol after suffering a series of arguably illegal hits from Denver. He was excellent against the Vikings to start Week 3, going 7-of-7 for 116 yards and a rushing touchdown before suffering an ankle injury on a sack and leaving the game briefly. When he came back, Newton went 14-of-28 for 146 yards. And on Sunday, Newton bizarrely lingered on the lip of the goal line while running in a two-point conversion before taking a lick from Deion Jones. Newton is now in the concussion protocol.

3. The Panthers' offense has failed to stay on schedule. We often think about the idea of staying on schedule as a team staying in manageable down-and-distances to avoid third-and-long. There's value in that, obviously, but the broader way to think about staying on schedule is this: Are you in a better position to score points after a play than you were beforehand? The expected points model that underpins the QBR metric does a good job of measuring that by accounting for down, distance and game situation.

Last year, 45.6 percent of Carolina's offensive plays added expected points to the ledger and increased its chances of scoring. That was the fourth-best rate in the league. This year, just 40.4 percent of the Panthers' plays have done the same thing. That's the sixth-worst rate in football. The Panthers have been just as effective on third down and even better in the red zone than they were a year ago, but what they've done outside of those situations just hasn't been enough on offense.

Much of that is also due to turnovers, which obviously can't improve your expected points total. Carolina's turnover rate on offense has skyrocketed from 9.6 percent last year (ninth in the league) to 18.8 percent (28th).

4. The secondary is struggling mightily. After allowing Julio Jones to go for 300 yards? You don't say! This isn't a one-week problem, though, and while Josh Norman would have helped, the problems go deeper than losing one cornerback. A closer look at the secondary suggests that there are major issues that will need to be worked out sooner rather than later.

The good news for Carolina is that it's still getting a lot of pressure. Last year, the Panthers bothered the opposing quarterback on 28.7 percent of dropbacks. Through four games this year, their pressure rate is at ... 28.7 percent. Not bad. That's the sixth-best rate in the NFL. The problem is when they don't get pressure. Last year, when the Panthers couldn't get pressure on the opposing passer, they were still third in the league in opposing passer rating and 11th in QBR. This year, when they leave the quarterback alone, Carolina is 19th in opposing passer rating and 28th in QBR.

What has changed for the Panthers is easiest to see with a heat map. These are two charts split into 10-yard chunks for air yards, the distance each pass travels in the air before landing. The heat measures opposing quarterbacks' relative passer rating against the Panthers in each zone versus that of other quarterbacks against other teams in those same zones. Red is good. Blue is bad. Black is neutral. Here's 2015's map:

Simple enough: The Panthers allowed quarterbacks to survive underneath, but when teams threw downfield, Carolina ate them alive. What about this year?

Oh boy. The chart has flipped. The Panthers are being carved up by teams attacking them downfield. Last year, on defending throws 11 or more yards in the air (the blue spots in 2015), the Panthers posted the league's best opposing QBR by 10 points (46.0), tied for the league's best passer rating (57.5), and allowed teams to complete only 41.2 percent of their passes while throwing 10 touchdowns against 16 picks.

This year, the Panthers are close to helpless downfield. Only the 49ers have allowed a worse QBR than Carolina's 99.0 mark. Sean McDermott's bunch is allowing a passer rating of 130.3 on those throws, with teams completing 68.3 percent of their passes and tossing up six touchdowns against two picks. Atlanta torched Carolina downfield in Week 4, but it was a problem even before Sunday; the Panthers were allowing a passer rating of 103.5 on those throws over the first three weeks.

It's still too early to break down the coverage issues in the Falcons game because the league won't post the All-22 film from the contest until tomorrow, but from replays, commentary and the few big plays which yielded coach's tape on replay during the game's broadcast, it's clear that there are communication and coverage lapses within the Carolina secondary. While there were plays in which Jones was simply too big and fast for any defender on the Panthers' roster, Carolina put itself in impossible situations and seemed to make as many mental mistakes as there were physical.

Start with this 43-yard bomb in the first quarter, which would have been a touchdown if Matt Ryan made a better throw over the top. (Ryan played well, but he left at least three would-be long touchdowns to Jones on the field with misplaced or underthrown deep passes.) I have to believe McDermott doesn't want to leave rookie cornerback Daryl Worley one-on-one on an island against Jones. And while Jones reduces Worley to dust at the line of scrimmage, after the play, Worley was shouting and pointing at safety Kurt Coleman, as if he was expecting help downfield.

On a first down in the second quarter, Jones beat Bene Benwikere over the top, but Ryan underthrew his pass and Benwikere was able to sprint at full stretch to tip it away. Two plays later, on third-and-17, Jones lined up in the slot and ran at full speed past Benwikere as the defender shuffled at half-speed. Jones ended up open by 5 yards downfield. Ryan's throw was poor and drew Jones into the middle of the field and in the line of fire of Coleman, but the result was a 53-yard gain. There's a coverage breakdown there which will be revealed by coach's tape, but the specifics are less important than the general problem: How on Earth do you end up with a coverage in which Jones is brutally uncovered downfield on third-and-17? Nobody does that on purpose.

The big plays to Jones later in the game were more about Jones' physical dominance and bad tackling. The soul-crushing 75-yard touchdown pass that got Jones to 300 yards came when the Falcons went with play-action and opened up the middle of the field. Jones beat Benwikere badly at the snap and shoved him aside after the catch, while deep safety Tre Boston took a terrible angle to the receiver and saw Jones accelerate right by him. Luke Kuechly even slowed down while he thought Benwikere was about to make the tackle. A great block downfield was enough to seal the touchdown.

One of Atlanta's other big plays also revealed a communication problem within the secondary. On the 48-yard touchdown pass to rookie tight end Austin Hooper, the Falcons went with play-action to the left and booted Ryan out to the right side of the field, a classic move in a Kyle Shanahan offense. Instead of throwing to the right side, though, Hooper feigned blocking before slipping out to the left side of the formation and running a go route. Not only did the Panthers totally switch off and fail to cover Hooper, but the view from the sky points out that they actually had two receivers open for big plays downfield:

Josh Norman might have been able to help with Julio Jones, but he can't cover both of those guys. And while I didn't really notice a lot of these issues in Week 3 against Minnesota, the Vikings don't really stretch teams vertically as often. Even against the middling 49ers passing attack in Week 2, the Panthers had trouble. Here's one example. Boston is again the deep safety on a second-and-9 just outside the red zone with Worley matched up in coverage against Torrey Smith. Despite the fact that Vance McDonald's crossing route is surrounded by no fewer than three Panthers defenders underneath, Boston sprints forward to try to break up any throw to the tight end, allowing Smith an easy release on his deep post for a touchdown. Here's the scene right after the ball is thrown:

And Boston wasn't the only safety who made a mistake to create an easy touchdown downfield. Coleman took a messy route to turn a short Vance McDonald catch into a 75-yard touchdown.

Will the Panthers figure it out? History suggests they will. McDermott and Ron Rivera have had to deal with this in the past. The secondary they inherited was a mess and they soon lost their best cornerback in Chris Gamble, who retired. They pieced together a useful unit from spare parts during Carolina's breakout season in 2013, but the cap-strapped Panthers were unable to retain Mike Mitchell and Captain Munnerlyn in free agency, while fellow starter Quintin Mikell retired.

The Panthers tried anew in 2014, but nothing worked for most of the year. Holdover Melvin White declined and was benched. Free agents Thomas DeCoud and Antoine Cason failed to impress and eventually lost their jobs late in the season. Norman, who had been lurking on the back of the roster, worked his way into a starting job and started to play like a Pro Bowler. Benwikere, a rookie fifth-rounder, got a shot out of sheer desperation and outplayed Cason.

Things clicked just in the nick of time for the Panthers. After Benwikere replaced the released Cason in the lineup for the final four weeks of the season, the Panthers went from allowing 27.6 points per game (and going 3-7-1) to allowing just 10.8 points over their final four contests, winning them all and claiming the NFC South. Norman emerged as a superstar, and Carolina's pass defense began to look like the suffocating unit which was so impressive last season. In 2014, though, it took the Panthers three-quarters of the year to get things right, and they were surprised to find that nobody else was particularly interested in winning the division.

If it takes them that long to piece together a functional secondary again in 2016, they might not be so lucky this time around.