A winning fantasy football roster needs a mix of blue-chip stars and under-the-radar sleepers who outperform their average draft positions. Managers can easily line up big-name playmakers in their draft queues, but what about the surprise contributors? 

Don't try to live your fantasy life on the waiver wire unless it's a last resort. Instead, spend some draft capital on a relatively unknown player or a veteran set for a bounce-back season who can fill a spot in your starting lineup throughout the year.

Managers can typically find such gems past the midway point of a 15-round draft.

We'll focus on standard point-per-reception Yahoo league settings, highlighting new and old names to watch with an average draft position of the eighth round or later based on Fantasy Football Calculator's metrics.

Before you shift into auto-draft mode in the latter rounds, make sure the following players and one particular defensive unit aren't left on the board.

QB Jimmy Garoppolo, San Francisco 49ers (12.03)

San Francisco 49ers quarterback Jimmy Garoppolo will have to stay healthy to outplay his 12th-round ADP. But if he does, the 27-year-old looks like an easy choice among league-winning sleepers.

Although Garoppolo has only 10 career starts, he's paired with a head coach who gives him major fantasy upside.

As an offensive coordinator, Kyle Shanahan worked with pocket passers like Matt Schaub, a 34-year-old Donovan McNabb at the tail end of his career and Matt Ryan. Each of those teams finished among the top 10 in passing yards.

As a first-time head coach in 2017, Shanahan started three quarterbacks under center: Brian Hoyer, C.J. Beathard and Garoppolo. The Niners finished ninth in passing that year.

After a tough start in the 2018 season opener, Garoppolo threw for 457 yards, four touchdowns and zero interceptions in the next two games. He isn't a scrambler, but he flashes an accurate arm with a career 65.4 percent completion rate.

Garoppolo have three pass-catching running backs in Matt Breida, Tevin Coleman and Jerick McKinnon, which should help them establish a strong short passing game. The Niners also selected wideouts Deebo Samuel and Jalen Hurd in the second and third rounds of this year's draft, respectively.

Garoppolo, who spent the 2014-16 seasons with the New England Patriots, compared Niners tight end George Kittle to Rob Gronkowski in an interview with Sporting News' Vinnie Iyer.

"There are a lot of similarities—on the field and a little bit off the field, too," Garoppolo said. "George is tremendous. The energy he brings every day, how he goes about his business—he's always having fun while he's doing it. Very similar to Gronk, they both enjoy what they do."

If Kittle builds on his breakout 2018 campaign, Garoppolo would have a solid pass-catching group with an innovative play-caller at head coach. That combination should result in a big year for the sixth-year veteran.

QB Mitchell Trubisky, Chicago Bears (13.07)

Chicago Bears quarterback Mitchell Trubisky experienced a breakthrough as a sophomore, throwing for 3,223 yards, 24 touchdowns and 12 interceptions under first-time head coach Matt Nagy.

Trubisky formed a solid rapport with Allen Robinson, Tarik Cohen, Taylor Gabriel, Trey Burton and Anthony Miller last season. Four of the five logged catch rates higher than 61 percent and are headed into their second year under Nagy.

This offseason, the Bears spent a fourth-round pick on wide receiver Riley Ridley, who put together a strong practice after missing the preseason opener against the Carolina Panthers, per WGNTV's Adam Hoge.

"Other than one drop, Riley Ridley is having a nice practice," Hoge tweeted. "Just went over Michael Joseph for a TD. Ridley looks healthy." 

The Bears also spent a third-round pick on running back David Montgomery and signed Mike Davis, both of whom can catch out of the backfield.

In 2018, Chicago's rushing offense ranked 11th and the aerial attack was 21st. Trubisky's natural growth and the addition of three capable pass-catchers should further elevate his numbers.

Don't forget, Trubisky also racks up fantasy points with his rushing ability. He recorded the fifth-most rushing yards (421) among quarterbacks and scored three rushing touchdowns last season.

RB Jaylen Samuels, Pittsburgh Steelers (10.03)

Pittsburgh Steelers running back Jaylen Samuels registered 2,958 yards from scrimmage and 47 total touchdowns during his four years at North Carolina State.

Steelers offensive coordinator Randy Fichtner seems primed to utilize that versatility.

According to The Athletic's Mark Kaboly, the Steelers think part of Samuels' skill set compares favorably to Le'Veon Bell.

"The Steelers have been so enamored with his route-running ability that a good chunk of their post-Antonio Brown offense has been modified to incorporate Samuels' best skills: running routes, catching footballs and creating mismatches. In fact, to some, Samuels' route-running skills are as good as, if not better than, Le'Veon Bell's."

No, Samuels won't lead the Steelers backfield—that's James Conner's role—but he could have a solid year as a pass-catcher following wideout Antonio Brown's departure. He converted 29 targets into 26 catches for 199 yards and three touchdowns last season.

Samuels could have a role similar to Patriots running back James White, who caught 87 passes for 751 yards and seven touchdowns in 2018. Keep an eye on him as a late-round option, particularly in PPR leagues.

RB Duke Johnson Jr., Houston Texans (12.04)

Earlier this month, the Houston Texans acquired running back Duke Johnson Jr. from the Cleveland Browns in exchange for a conditional 2020 fourth-round pick.

He'll sit behind Lamar Miller on Houston's depth chart, but he landed in a better spot for fantasy purposes.

Through four seasons in Cleveland, Johnson averaged 4.7 carries per game and never logged more than 104 rushing attempts in a season. In Houston, he's potentially primed to get 10-12 touches as a ball-carrier along with a handful of receiving targets per game.

Over the last two seasons, Miller has averaged 14.9 and 15 carries per game, respectively, which leaves room for Johnson to take on a portion of the rushing workload.

Although Miller can catch out of the backfield, the Texans should look to utilize Johnson in that role. He logged at least 47 receptions in all four of his seasons with the Browns.

Since 2016, Miller has only 13 scores on the ground. Because of his infrequent end-zone trips, Johnson may become a touchdown vulture.

With a 12th-round ADP, he's worth a pickup late in the draft.

WR Marquez Valdes-Scantling, Green Bay Packers (8.12)

Fantasy managers should leave a roster space open for a Green Bay Packers wide receiver other than Davante Adams.

Marquez Valdes-Scantling played only a few snaps in Week 1 of the preseason against the Texans, but he's put together a strong offseason.

According to Ryan Wood of the Green Bay Press-Gazette, Valdes-Scantling has a lead on Equanimeous St. Brown for the No. 2 spot on the depth chart.

"Feel like the WR competition is just getting started," Wood tweeted, "but right now Marquez Valdez-Scantling is pretty clearly ahead of EQ St. Brown as the second perimeter WR across Davante Adams. (Geronimo Allison in the slot.) Will that continue the next five weeks? Way too early to know."

In an interview with NFL Network's James Jones, Rodgers mentioned Valdes-Scantling as someone who jumped out during offseason practices.

Last season, Valdes-Scantling finished third in targets (73) and receiving yards (581) in 16 contests, which included 10 starts. He has a foundation with quarterback Aaron Rodgers to build upon.

So long as the 24-year-old holds on to a primary spot in three-wideout sets, he should have a solid year as a WR3 or flex asset. 

WR Tyrell Williams, Oakland Raiders (12.05)

With Derek Carr under center, the Oakland Raiders' No. 2 wideout has held a decent role in the passing offense, logging at least 666 receiving yards every season. The five-year signal-caller goes through his reads and isn't shy about spreading the ball.

Last year, running back Jalen Richard and tight end Jared Cook led the team in receptions (68).

With that context in mind, fantasy managers shouldn't overlook Tyrell Williams just because of Antonio Brown. Expect the former to see a healthy number of targets alongside the four-time All-Pro wide receiver.

Brown has yet to fully heal from a foot injury stemming from a mishap in a cryogenic chamber. In addition to his frostbitten feet, he's had issues with a new helmet, according to The Athletic's Vic Tafur.

"Brown has worn the same helmet for the last decade, and reportedly thinks the new one affects his vision when he is trying to catch the ball," Tafur wrote.

Brown's foot injury may heal in time for Week 1 and he might adjust to his new helmet, but those are two question marks that could affect his production. 

Williams can play all three wide receiver positions, which makes him compatible in head coach Jon Gruden's complex offense. He's also a big-play wide receiver who averaged 16.3 yards per catch through four years with the Los Angeles Chargers. 

Carr's tendency to cycle through his receiving options, Brown's recent issues and Williams' skill set should equate to a solid year for the 27-year-old. 

Even if Brown goes into the year healthy, Williams is a great value in the double-digit rounds.  

TE Delanie Walker, Tennessee Titans (11.12)

Since Marcus Mariota took over at quarterback for the Tennessee Titans in 2015, Delanie Walker has led the team in catches (237), receiving yards (2,747) and receiving touchdowns (16).

Yes, Walker suffered a broken ankle with ligament damage in Week 1 of the 2018 season and is going into his age-35 campaign, but Jim Wyatt of the team website believes he "will be ready for the start of the season." 

Before the injury, Walker earned three consecutive Pro Bowl invites, coinciding with Mariota's arrival in Tennessee.

New Titans offensive coordinator Arthur Smith served as a tight ends coach in some capacity for the past six years. His knowledge of the position likely bodes well for Walker's involvement in the passing offense.

The Titans bolstered their wide receiver corps this offseason, signing Adam Humphries and selecting A.J. Brown in the second round of this year's draft. However, neither of them have ready-made chemistry with Mariota, while 2017 No. 5 overall pick Corey Davis hasn't experienced his breakout campaign yet.

Among the Titans pass-catchers, fantasy managers should go with a proven commodity in Walker.  

DEF Pittsburgh Steelers (14.09)

Remember when the Steelers consistently ranked among the top 10 in yards and points allowed earlier in quarterback Ben Roethlisberger's career?

That could happen again this season.

Last year, the Steelers defense ranked 14th in Yahoo fantasy points (116), which reflects a middle-of-the-pack group that was 16th in scoring and sixth in yards allowed.

During the offseason, general manager Kevin Colbert added two defensive assets: four-year cornerback Steven Nelson and rookie first-rounder Devin Bush.

Nelson had his best year in 2018, logging 15 pass breakups and four interceptions. He seems equipped to man the perimeter opposite Joe Haden, strengthening the secondary.

Bush put together an impressive showing against the Tampa Bay Buccaneers in Week 1 of the preseason, registering 10 total tackles and seven solo takedowns. Although he didn't snag an interception or tally a sack, the Michigan product provides much-needed quickness to a defense that misses Ryan Shazier at inside linebacker.

The additions at cornerback and linebacker mixed with an aggressive defense that's ranked or tied for first in sacks over the last two years should result in a moderate improvement in fantasy value.

Assuming the Steelers give up fewer points with better coverage and sideline-to-sideline speed, Pittsburgh's defensive unit could finish among the top eight in fantasy points.

Unless otherwise indicated, all stats are courtesy of Pro Football Reference. Average draft positions are courtesy of Fantasy Football Calculator.