The 2020 NFL season has featured a lot of injuries and disappointments for fantasy managers, but some sleepers and waiver-wire pickups have taken the league by storm.

Top fantasy draft picks like Saquon Barkley, Christian McCaffrey, Michael Thomas and others have suffered injuries that led to long-term absences, dealing huge blows to fantasy teams. However, that has created opportunities for breakout seasons from some relatively unknown names.

As the halfway point of the season approaches, let's reflect on players who have exceeded expectations or been major disappointments based on their average draft positions. It's not totally fair to evaluate players who have suffered serious injuries, but those who have performed well after injuries to teammates deserve consideration.

Here are this year's biggest risers and fallers in fantasy football at each of the skill positions.

Riser: Justin Herbert (QB, Los Angeles Chargers)

For someone who wasn't a Week 1 starter, Los Angeles Chargers rookie quarterback Justin Herbert has quickly turned into a legitimate fantasy football asset.

A first-round pick in April, Herbert was expected to sit behind journeyman quarterback Tyrod Taylor while getting acclimated to the pro level. Instead, a pregame injury to Taylor in Week 2 forced Herbert to make his first career start against the Kansas City Chiefs.

While the Chargers have yet to win a game with Herbert, the rookie has played well enough to be named the team's starter going forward.

From a fantasy perspective, Herbert's production through four games has made him a starting-caliber option. He's completed 68.8 percent of his passes for 1,195 yards, nine touchdowns and three interceptions for a passer rating of 107.1. He's put up at least 20 fantasy points in all but one game he's started.

Herbert's ADP had him as the 36th quarterback taken in standard leagues, making him an irrelevant fantasy option at the beginning of the year. Now, the former Oregon quarterback is a front-runner to win this year's Offensive Rookie of the Year Award, as well as a borderline QB1 option for fantasy managers.

Faller: Lamar Jackson (QB, Baltimore Ravens)

While Baltimore Ravens quarterback Lamar Jackson isn't playing poorly, fantasy managers who drafted the reigning MVP were hoping for more out of him through six games.

Jackson had an ADP of 17th overall in standard leagues as managers expected big plays through the air and on the ground. While the Ravens are 5-1, Jackson's production has taken a dip compared to 2019. His 21 fantasy points per game rank just 11th among quarterbacks.

That regression in fantasy production should have been expected. Jackson had five games last season with at least four total touchdowns, as well as five games with at least 100 rushing yards. He has yet to register a four-touchdown game in 2020 and has only eclipsed 100 rushing yards once.

Opposing defenses are making an effort to contain Jackson, but the Ravens are also trying to get their running backs involved. Mark Ingram II, Gus Edwards and rookie J.K. Dobbins have already run the ball 123 times for 597 yards and five touchdowns. That committee in the backfield should allow all three to stay fresh despite a heavy dose of rushing attempts.

Jackson might be able to bounce back after the Week 7 bye, but his next two games will be against stingy defenses in the Pittsburgh Steelers and Indianapolis Colts. Both rank in the bottom five of fantasy points allowed to opposing quarterbacks.

Riser: Mike Davis (RB, Carolina Panthers)

The injury to Christian McCaffrey has been devastating for some fantasy managers, but those who were able to pick up Mike Davis have benefitted from one of the biggest breakout players of the year.

Davis has become a productive back for the Panthers since McCaffrey suffered an ankle injury in Week 2. Surprisingly, he has done a good job replacing McCaffrey as both a runner and receiver, racking up 32 receptions for 209 yards and two touchdowns to go along with 272 yards and two scores on the ground.

What's impressive is that despite not registering a carry or reception in Week 1, Davis is averaging 17 fantasy points per game, making him the 10th-highest-scoring running back in PPR leagues. Ignoring a zero-point performance in Week 1, Davis is averaging 20.4 fantasy points over the last five games.

McCaffrey is getting closer to returning but isn't expected to play this week against the New Orleans Saints. Even when the superstar running back returns, Davis has done enough to maintain a workload within the Panthers offense.

Considering Davis was the 94th running back drafted on average in PPR leagues, he has been one of the best waiver-wire pickups of the year for fantasy managers.

Faller: Cam Akers (RB, Los Angeles Rams)

Drafting a running back on a team that uses a by-committee approach can be a risk. Unfortunately for fantasy managers who were high on Cam Akers, the rookie has struggled to carve out a larger role in the Los Angeles Rams offense.

Akers was the first player taken by the Rams in the 2020 NFL draft. Coming out of Florida State, the rookie put up 3,361 yards and 34 touchdowns from scrimmage in three college seasons, and fans hoped he could bring that kind of production to the Rams backfield.

He had an ADP in the top 60 overall in PPR leagues, and managers had high hopes after he carried the ball 14 times and caught a pass in Week 1. The workload was solid, but the production wasn't there as Akers picked up only 43 total yards.

A rib injury in Week 2 kept Akers sidelined until Week 5, and by then Darrell Henderson Jr. had established himself as the team's top running back. Akers didn't register a carry or reception this past week against the San Francisco 49ers behind both Henderson and Malcolm Brown on the depth chart.

Without any kind of workload in Week 6, it may take some time for Akers to work his way back into the Rams offense, and that's tough for fantasy managers who drafted him.

Riser: DK Metcalf (WR, Seattle Seahawks)

Once thought to be a potential draft bust, Seattle Seahawks wide receiver DK Metcalf has developed into a fantasy football star, not only for the 2020 season but beyond.

After a promising rookie season where Metcalf posted 900 receiving yards and seven touchdowns, the second-year Seahawks receiver has taken his game to a whole new level. In five games, he's caught 22 passes for 496 yards and five touchdowns, leading the NFL with 22.5 yards per reception.

Metcalf's big-play potential has turned him into one of the most valuable fantasy receivers in the league. His 19.9 fantasy points per game in PPR leagues is the fourth-highest mark among wide receivers.

Fantasy managers couldn't be happier with Metcalf, especially considering his ADP had him as the 22nd receiver drafted on average in PPR leagues. His consistency has also been a relief, as he's posted at least 14 fantasy points in every game.

Quarterback Russell Wilson is having an MVP-caliber season thanks to Metcalf and fellow star receiver Tyler Lockett. The talent around Metcalf has opened things up for him in Seattle, and his production has him on pace to be a Pro Bowl and All-Pro candidate.

Faller: T.Y. Hilton (WR, Indianapolis Colts)

The Indianapolis Colts are sitting at 4-2 thanks to a strong running game and a defense capable of making game-changing plays. However, wide receiver T.Y. Hilton hasn't been a big contributor for the offense.

A four-time Pro Bowler from 2014 through 2017, Hilton has had a quiet start to the season with only 20 catches for 242 yards and zero touchdowns. While he's never had more than seven touchdowns in a season, he also hasn't had fewer than four, so his absence from the end zone is concerning.

Fantasy managers who drafted Hilton are particularly concerned. The Colts wide receiver had a top-60 overall ADP in PPR leagues, yet Week 5 against the Cleveland Browns was his only game in 2020 with double-digit fantasy points.

The Colts have felt more comfortable establishing a run game with Jonathan Taylor and Nyheim Hines. Hilton is still first on the team with 37 targets, but that mark ranks just 34th overall in the NFL.

That has had a negative impact on Hilton's production. Given the way the Colts offense has played, it's not likely the 30-year-old will be much of a fantasy asset moving forward.

Riser: Robert Tonyan (TE, Green Bay Packers)

The Green Bay Packers have a crowded depth chart at tight end as Robert Tonyan, Marcedes Lewis and Jace Sternberger compete for snaps. While none of those players were appealing fantasy options heading into the season, Tonyan has established himself as one of the top fantasy tight ends in the league through six weeks.

He is tied for the league lead among tight ends with five touchdown receptions. While he has 16 catches overall for 198 yards, finding the end zone has made him a valuable player in fantasy.

Although he didn't have a catch in Week 1, Tonyan is the sixth-highest-scoring tight end in PPR leagues with an average of 13.2 points per game. That's inflated thanks to his three-touchdown game against the Atlanta Falcons in Week 4, but he still had a three-week streak of double-digit fantasy performances.

Tonyan cooled off this past week, catching three passes for 25 yards, but he's developed a lot of trust with Aaron Rodgers, especially near the end zone. Considering he came into this season as an unknown commodity, his five touchdowns already easily makes him the biggest fantasy riser among tight ends in 2020.

Faller: Zach Ertz (TE, Philadelphia Eagles)

After an offseason that included some disagreements over a potential contract extension, Philadelphia Eagles tight end Zach Ertz hasn't done much in 2020 to warrant another big payday.

Ertz got off to a strong start, catching a touchdown pass in Week 1 against the Washington Football Team. He was averaging 11.3 fantasy points per game in PPR leagues through the first three weeks of the season, but his production has dropped off. Over the past three games, he's only caught nine passes for 48 yards.

His workload should have increased with the injury to fellow tight end Dallas Goedert in Week 3. Instead, the absence of Goedert has made it even harder for Ertz to get open and make plays for the Eagles offense.

Now, Ertz is expected to be out between three and four weeks with an ankle injury. For someone who was the fourth tight end drafted on average, he's been the most disappointing fantasy player at the position in 2020.

All ADP info provided by FantasyPros.