Every team wants one: a shutdown cornerback they can leave isolated on the sideline to shadow and ultimately shut down the opposition's top receiving threat. But shutdown corners are hard to find. Most often, you need to draft and develop them. Sometimes, like the Jaguars did with A.J. Bouye a year ago, you can get lucky by plucking one away from another team in free agency.

And that brings us to the 2018 free agent class of defensive backs, an intriguing group that includes a star cornerback, a former Super Bowl hero coming off a strange ending to his career in New England, a versatile safety, and a former CB1 who is coming off a puzzling ending to his career in Indianapolis. Welcome to your primer for the defensive back free agent class of 2018.

Let's break down all the defensive backs who will be available on the open market this offseason from Trumaine Johnson to Malcolm Butler to LaMarcus Joyner to Vontae Davis (remember him?). Below, you'll find all the names you need to know in this group. If you want the entire (long) list, head on over to Spotrac. They've got all the numbers and data you need for this year's group of cornerbacks and safeties.

OK, onto our list. We begin with Trumaine Johnson.

The headliner

Trumaine Johnson -- CB

This is actually Johnson's third straight uncertain offseason after the Rams opted to use the franchise tag on him the past two years. In doing so, the Rams made Johnson the first defensive back to get the franchise tag in consecutive seasons since Charles Woodson in 2004-05, according to NFL Research.

This time, the Rams likely won't franchise tag him again. That doesn't mean he won't return to Los Angeles. The Rams will likely be interested in locking him up for the long-term. But considering their reluctance to sign him to a long-term deal in the past two offseasons, it really wouldn't be surprising to see him leave in free agency. 

Johnson, 28, should garner plenty of interest. He's the main headliner after all -- and with good reason. Over the past three seasons, he's snagged 10 interceptions, two of which he returned the distance, and recorded 41 pass breakups. In 2015, he allowed a 55.0 passer rating in coverage -- second among qualified cornerbacks -- according to Pro Football Focus. In 2016, he allowed an 89.4 passer rating in coverage, which ranked 34th. And this past season, he allowed a 79.8 passer rating in coverage, which ranked 36th. He might not be a top-five cornerback, but he's in the top-tier. Someone is going to pay him like it.

Co-headliners

Malcolm Butler -- CB

Oh where to begin with Butler? He's an undrafted player whose career essentially began in Super Bowl XLIX when he picked off Russell Wilson at the goal line to preserve the Patriots' fourth Super Bowl under Bill Belichick. He spent the next few seasons as a starter and put up pretty solid numbers along the way, proving he wasn't just a one-play wonder.

In 2015, Butler picked off two passes, broke up 15 passes, and allowed a 97.5 passer rating in coverage, according to PFF. In 2016, Butler snagged four picks, defended 16 passes, and allowed a 78.2 passer rating in coverage. In 2017, Butler notched two interceptions, defended 12 passes, and allowed a 96.6 passer rating in coverage. In the lead up to the Super Bowl, he called his season "s----y," but even he couldn't have seen what was coming next. Butler didn't play a single defensive snap in the Super Bowl, getting benched and watching from the sidelines as the Patriots got burned for 41 points by a Nick Foles-quarterbacked offense. An explanation for his mysterious benching still hasn't emerged.

And so, that will likely end Butler's career with the Patriots. Unlike last year, when he was a restricted free agent, Butler, 27, will be free to leave. He will have plenty of suitors regardless of the reasoning behind his Super Bowl benching, namely because he's a good, if not great cornerback. Heck, Texans receiver DeAndre Hopkins has already started courting him. 

Let the bidding begin on a player who's never made good NFL money in his career.

Lamarcus Joyner -- FS

The Rams might not just lose Johnson. They also could lose a starting-caliber safety in Joyner.

Joyner, 27, was used by Jeff Fisher as a nickel cornerback, but under new defensive coordinator Wade Phillips, he moved to safety so that he could be on the field more frequently. It worked.

"We came in, we watched the film from the year before and we said, 'This guy's one of our best players and he only played half the time -- what should we do?'" Rams defensive coordinator Wade Phillips said in December, per ESPN. "We said, 'Well, let's play him all the time then.' It sounds simple, but he's too good a player not to be on the field, in my opinion. And he thought the same way. I saw 'Hard Knocks.' I think he felt the same way."

In 12 games, Joyner snagged three picks, one of which he returned for a touchdown, broke up nine passes, and racked up 39 solo tackles. He was PFF's third-highest graded safety, posting the highest coverage grade among his peers. As a result, he'll be the most-coveted safety in free agency.

A mystery with upside

Vontae Davis -- CB

Not too long ago, Davis, 29, was a shutdown corner for the Colts. From 2009-16, he appeared in 115 games with 107 starts and totaled 22 interceptions. He went to the Pro Bowl in 2014 and 2015. Davis was the league's second-best cornerback in 2014 behind Chris Harris Jr., according to PFF. But his production slipped in recent seasons. He ranked 24th in 2015, 113th in 2016, and 84th in five appearances in 2017. 

In November, Davis discovered he needed season-ending groin surgery. Then, he was shockingly released by the Colts. He wasn't happy about the entire situation. He thought he was benched earlier in the season because he wasn't healthy while then coach Chuck Pagano claimed he benched him because of his quality of play.

"It should be more about the respect," the cornerback said, per IndyStar.com. "I'm a professional. I've been in [the league] long enough. When I look at the situation, I feel like there was no respect. Knowing Chuck, I figured it would come from him. It really bothered me."

Davis will be 30 before next season begins. Someone will likely take a chance on him, hoping that he can rediscover the magic from the earlier portion of his career.

Solid options

Brent Grimes -- CB

At 34, Grimes submitted another impressive season for the Buccaneers. Since 2013, he's averaged four interceptions per season. In the past two seasons, Grimes has intercepted seven passes. In 2017, he allowed a 73.8 passer rating in coverage, which ranked 20th among his peers, according to PFF. Grimes is still a good player, but his age is concerning. Still, someone will likely scoop him up on a one or two-year deal. He'd be perfect for a contender lacking a second starting cornerback.

Kyle Fuller -- CB

Fuller's experienced a topsy turvy career to this point, but he's seemingly peaking again. A first-round pick of the Bears back in 2014, Fuller exploded at the beginning of his rookie season, snagging three interceptions in his first three games. And then he faded away. After a poor 2015 season, he missed all of 2016 with an injury. He returned on shaky ground in 2017 for what appeared to be his final season in Chicago. 

Very quietly, Fuller pieced together a quality season with two picks, a career-high 22 passes defended, and a very nice 69.0 passer rating in coverage, which ranked 14th among qualified cornerbacks, according to PFF. Nobody will mistake Fuller for a shutdown corner, but if he keeps this up, he'll cement his status as a good, not great cornerback. 

At this point, the most obvious landing spot for Fuller is Chicago. The Bears are short on cornerbacks and they're already familiar with Fuller. They should make re-signing him a priority.

Bashaud Breeland -- CB

He's been overshadowed by the louder and better Josh Norman, but Breeland has developed into a capable corner. He's only 26. He's been durable, appearing in 60 of 64 possible games. He's averaged two interceptions per season. This past season, he allowed a 75.6 passer rating in coverage and graded out as PFF's 54th best cornerback -- one spot behind Norman. 

According to NBC Sports Washington's JP Finlay, the Redskins will let him test free agency.

Morgan Burnett -- SS

For the Packers last season, Burnett played in 12 games, failed to register an interception, and graded as PFF's 47th best safety. He's not flashy. He's 29. But he's experienced and could be a nice backup on a loaded team or a starter on a desperate team. He has nine career interceptions.

Eric Reid -- FS

The former first-round pick of the 49ers would be a solid pickup in free agency after a 2017 season that saw him register two interceptions in 13 games and rank 30th among all safeties, according to PFF. Like Burnett, he's experienced, but not yet too old at 26, and should garner some interest on the open market. He can still be a starter.

Prince Amukamara -- CB

Amukamara signed a one-year, prove-it type of deal with the cornerback-desperate Bears in the offseason and well, he proved his ability to be a decent, but not great cornerback. He missed only two games, defended seven passes, allowed an 89.1 passer rating in coverage, and failed to land an interception. If the Bears don't bring back Fuller, they might target Amukamara instead.  

Terence Newman -- CB

Age is the primary concern when it comes to Newman. The 39-year-old finally showed slight signs of aging with the Vikings this past season, allowing a 76.7 passer rating in coverage, which ranked 29th among cornerbacks. As my colleague Jared Dubin put it, "That's basically the equivalent of being Brock Osweiler on every pass." In 2016, Newman experienced an incredible season, allowing the fifth-lowest passer rating in coverage (62.0). 

At this stage in his career (he'll turn 40 in September), Newman shouldn't be handling a full workload (his 359 coverage snaps in 2017 ranked 72nd among cornerbacks, per PFF), but he's the best rotational player on this list. Mike Zimmer is a big fan of Newman, having already offered him a job on his coaching staff, so don't be surprised to see him return to Minnesota where he's a perfect fit on a loaded defense.

Tre Boston -- FS

Boston, 25, exploded with the Chargers in 2017, racking up five interceptions and eight passes defended, and grading as PFF's 30th best safety. He's not much of a run stopper, but can be an impact player against the pass.

Tyvon Branch -- SS

Branch, 31, failed to register an interception in nine games, but he defended six passes and racked up 51 tackles. More importantly, PFF graded him as the sixth-best safety. Nobody will be giving him a hefty contract, but he can still help a team.

Others worthy of recognition:

  • Ricardo Allen -- S
  • Marcus Gilchrist -- SS
  • Rashaan Melvin -- CB
  • E.J. Gaines -- CB
  • Bryce Callahan -- CB
  • Patrick Robinson -- CB

The entire class

In all, there are 118 secondary players available this offseason, according to Spotrac. Some names you might recognize:

Here's the entire list sorted alphabetically (via Spotrac) ...

Position

Age

Status

Kenneth Acker 

CB

26

UFA

Jude Adjei-Barimah

CB

25

RFA

Walt Aikens 

FS

26

UFA

Nate Allen

FS

30

UFA

Ricardo Allen 

SS

26

RFA

David Amerson

CB

26

UFA

Prince Amukamara 

CB

28

UFA

Colt Anderson

SS

32

UFA

Johnson Bademosi 

CB

27

UFA

Keith Baxter

CB

25

ERFA

Bene Benwikere

CB

26

UFA

Nat Berhe 

SS

26

UFA

Justin Bethel 

CB

27

UFA

Tre Boston

FS

25

UFA

Brandon Boykin

CB

27

UFA

Tyvon Branch

SS

31

UFA

Delvin Breaux

CB

28

RFA

Bashaud Breeland

CB

26

UFA

Tramaine Brock 

CB

29

UFA

Terrence Brooks

FS

26

UFA

Donatello Brown

CB

26

ERFA

Morgan Burnett

SS

29

UFA

Rafael Bush

FS

30

UFA

Darius Butler

FS

31

UFA

Macolm Butler 

CB

27

UFA

Jairus Byrd

FS

31

UFA

Bryce Callahan 

CB

26

RFA

Don Carey 

SS

31

UFA

Travis Carrie 

CB

27

UFA

Morris Claiborne 

CB

28

UFA

Ross Cockrell 

CB

26 

UFA

Justin Coleman 

CB

24

RFA

Aaron Colvin 

CB

26

UFA

Cody Davis 

FS

28

UFA

Pierre Desir 

CB

27

UFA

Greg Ducre

CB

26

RFA

Nate Ebner

FS

28

UFA

Javien Elliott

CB

24

ERFA

Deshazor Everett 

SS

25

RFA

Antone Exum 

FS

26

UFA

Kyle Fuller 

CB

25

UFA

E.J. Gaines 

CB

25

UFA

Phillip Gaines

CB

26

UFA

Marcus Gilchrist 

SS 

29

UFA

Demetri Goodson 

CB

28

UFA

C.J. Goodwin 

S

28

ERFA

Corey Graham 

FS

32

UFA

Brent Grimes

CB

34

UFA

LaDarius Gunter

CB

25 

RFA

DeAngelo Hall

CB 

34

UFA

Leon Hall

CB

33

UFA

Anthony Harris 

SS

26

RFA

Erik Harris

CB 

27

ERFA

D.J. Hayden 

CB 

27

UFA

Troy Hill

CB

26

ERFA

Davon House 

CB

28

UFA

Kemal Ishmael 

SS

26

UFA

Asa Jackson

CB

28

UFA

Stanley Jean-Baptiste 

CB

27

ERFA

Dontae Johnson 

CB

26

UFA

Isaiah Johnson FS 25 UFA

Leonard Johnson 

CB 

27 

UFA

Trumaine Johnson 

CB

28 

UFA

Johnathan Joseph 

CB

33

UFA

LaMarcus Joyner 

FS 

27 

UFA

Brandon King 

FS

24

RFA

Nevin Lawson 

CB

26

UFA

Jordan Lucas 

S

24

ERFA

Byron Maxwell

CB

29

UFA

Brice McCain

CB

31

UFA

Robert McClain

CB 

29

UFA

Bradley McDougald 

SS

27

UFA

Leon McFadden

CB

27

UFA

Keith McGill 

S

28

UFA

Sherrick McManis 

CB

30

UFA

Rashaan Melvin

CB

28

UFA

Doug Middleton 

S

24

ERFA

Rontez Miles 

FS

29

RFA

Chris Milton 

CB

25

ERFA

Terrance Mitchell

CB

25

RFA

Corey Moore

SS

25

ERFA

Sterling Moore

CB

28

UFA

Darryl Morris

CB

27

UFA

Sharrod Neasman

S

26

ERFA

Reggie Nelson 

FS

34

UFA

Terence Newman 

CB

39

UFA

Adrian Phillips 

FS

25

RFA

Lafayette Pitts

CB

25

ERFA

Eddie Pleasant 

FS

29

UFA

Eric Reid 

SS

26

UFA

Darrelle Revis

CB

32

UFA

Curtis Riley

CB

25

ERFA

Nickell Robey-Coleman

CB

26

UFA

Patrick Robinson 

CB

30 

UFA

Deshawn Shead 

FS

29 

UFA

Marcus Sherels 

CB

30

UFA

Jordan Simone 

S

25

ERFA

C.J. Smith

CB

24

ERFA

Daimion Stafford

SS

26

UFA

Keith Tandy

FS

29

UFA

Steven Terrell

CB

27

UFA

Michael Thomas

FS

28

UFA

Shamarko Thomas 

SS

27

UFA

Peyton Thompson 

SS

27

UFA

Kenny Vaccaro 

SS

26

UFA

Alterraun Verner 

CB

29

UFA

T.J. Ward 

SS

31

UFA

Jaylen Watkins

S

25

RFA

B.W. Webb

CB

28 

UFA

Jermaine Whitehead 

FS 

24

ERFA

Marcus Williams

CB

26

UFA

Teddy Williams

CB

29

UFA

Tramon Williams

CB

34

UFA

Trevor Williams 

CB

24

ERFA

Tavon Wilson 

SS

27

UFA

Blidi Wreh-Wilson 

CB

28 

UFA

Shareece Wright 

CB 

30

UFA

Ronald Zamort

CB

26

 ERFA