Mark Humphrey/Associated Press

Over the last nine months, our team of Dan Bazal, Marshal Miller and myself sat down to study and evaluate the best college football players in the country. There was no set number of players to watch—our goal was simply to scout, grade and rank the seniors and draft-eligible underclassmen who would be NFL caliber.

That number ended up at 400—actually 441—which is where the NFL Draft 400 series comes in.

The goal of the Draft 400 was to introduce you, the reader, to the best players available in this year's class. There are only 256 picks in the NFL draft, but with undrafted free-agent signings accounting for another 100 or so players, this list of 400 should cover every base come draft weekend. And if not—if the Green Bay Packers draft a kicker from Southwest Baptist University—our apologies.

This was a three-man operation compared to the 10- to 15-person scouting department each NFL team employs. And the result is one we're happy with. So here they are, the top 400 players in the 2015 draft class, ranked 400 to 1.

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At the end of each scouting report, you'll see a final grade that falls somewhere between 4.00 and 9.00 on a unique grading scale. This scale comes from the teaching I received from Charley Casserly, Michael Lombardi and other former and current front office personnel in the NFL. I've tweaked it this year to be more transparent, and the result is each player receiving a number grade as well as his ranking.

This applies to all positions across the board.

Brynn Anderson/Associated Press

Players ranked 400 to 300...these are the undrafted free agents and some seventh-rounders.

If your favorite team takes one of the prospects listed here and turns him into a Pro Bowler, well, you can be dang proud of that one. Guys with a grade below 5.00 are considered priority free-agent material—that means don't draft them, but sign them as Day 3 of the draft ends.

Players at 5.00 are the late-rounders. And there are a few potential stars here. These are guys missing one or two traits, but they have tools that can be developed. Memorize this list, because in three years there's a good chance we'll all go back to look and see which undrafted free agent became a star.

Chris O'Meara/Associated Press

Players 299 to 200 encompass a big part of Day 3 of the 2015 NFL draft. Here you'll find kickers, quarterbacks, punters, a ton of wide receivers and edge-rushers and good offensive line depth.

This isn't an area to take lightly, either, as every player on this page has a draftable grade (5.00) or higher. Super Bowls are won with depth, and teams like the New England Patriots, Seattle Seahawks and Baltimore Ravens have owned their scouting of the types of prospects you see here.

Gerry Broome/Associated Press

Players 199 to 100...now we're getting into the meat of the draft class. There will be Pro Bowlers. There should be an All-Pro, if draft history holds to form. There might even be a Hall of Famer.

Players ranked here are graded between 5.20 (priority backup) and 5.50 (rookie impact/future starter), so much is expected. All of the prospects listed below should contribute as a rookie as long as they are healthy.

Generally, a guy ranked here is one or two traits away from being a top-100 player. Maybe it's a 40 time that was too slow, an off-field issue or a lack of ideal size for the position. But Russell Wilson was ranked in this range, and he's turned out to be pretty dang good.

Mark Wallheiser/Associated Press

These are the kingmakers. Hit on your picks in the top 100, and you can have a starter in every round. The players here vary greatly—from rookie impact (5.50) to expected Pro Bowlers (7.50). It's important to look at the grade as much as the ranking, and that's why it's listed first.

Four prospects tied for the top overall grade: Jameis Winston, Leonard Williams, Dante Fowler and Kevin White (with Amari Cooper so close behind). The top of this draft is solid, but there's no "sure thing" Andrew Luck or Khalil Mack-type player here. 

Eric Gay/Associated Press

The 2015 quarterback class isn't much to write home about, but the top two players are very good.

Jameis Winston received the fourth-highest quarterback grade I've assigned (behind Andrew Luck, Robert Griffin III and Teddy Bridgewater) and has legitimate franchise QB tools. Marcus Mariota is a special person and special athlete, but he'll face a big test in acclimating to the NFL.

The same goes for Bryce Petty, who isn't as athletic as Mariota but has a cannon for a right arm. 

John Bazemore/Associated Press

The running back class is one of the best ever, and with that in mind, we should see two ball-carriers selected in the first round: Todd Gurley and Melvin Gordon. Each player is worth it if you look at his draft grade outside of position value, but there will be critics of selecting a running back in Round 1 when the draft is this deep at the position.

Look at the list below and you'll notice nine running backs have a starter or future starter grade. It's a good year to need a back, and teams will be able to find starters in Rounds 2 and 3.

Butch Dill/Associated Press

As you might expect, the fullback position has been devalued in recent years. In fact, 2014's draft included only three fullbacks: Jay Prosch (sixth round), Kiero Small (seventh) and Trey Millard (seventh).

Gone are the days of Mike Alstott, but Alabama's Jalston Fowler is someone to watch. He averaged 6.6 yards per carry over his collegiate career, and he proved to be a factor in the red zone.

Butch Dill/Associated Press

The 2015 wide receiver class cannot compete with the historic 2014 class, but that's OK. This is still a very good group headlined by three future stars and anchored by huge-potential players littered throughout the first three rounds.

Any team needing a wide receiver has to feel good about this crop. Kevin White, Amari Cooper and DeVante Parker all have blue-chip potential. If you can get past the off-field issues and rawness of Dorial Green-Beckham, you'll find a player with an unmatched ceiling.

Add in the pure speed of Breshad Perriman and the big-play ability of Nelson Agholor, and there are five legitimate first-round wide receivers. Not bad for any year. The depth here is remarkable, and that's not counting the one or two sleepers who come out of nowhere (hello, Allen Hurns) to become studs.

Joel Auerbach/Associated Press

Quite unlike the fullback position, tight ends are a huge part of modern NFL offenses. Top targets like Jimmy Graham and Rob Gronkowski have changed the game with their ability to stretch the field.

There might not be any Grahams or Gronkowskis in this draft, but Maxx Williams, Clive Walford and Wes Saxton could all make impacts at the next level. Another guy to watch is converted QB Blake Bell, who has ideal size for the position but is understandably raw.

Marcio Jose Sanchez/Associated Press

The player most likely to be selected first at offensive tackle—Andrus Peat—isn't the top-ranked prospect at the position, but that's how it tends to go with this group. Peat has athleticism, length and upside, and that'll get you drafted high if you can protect the left side of the line.

Peat, D.J. Humphries and Jake Fisher are all special pass protectors, and throw in La'el Collins and Cedric Ogbuehi as top-tier run blockers, and you have five tackles with legitimate Round 1 talent. That's great news for some lucky team at the top of the second round, as it's likely someone will fall.

Charlie Neibergall/Associated Press

Iowa's Brandon Scherff headlines the position this year, yet a small-school prospect could steal the show: Hobart's Ali Marpet. Not only is Hobart a tiny school, it's Division III.

Interestingly, according to The Boston Globe, Marpet "entered college at 255 pounds, and because of the weight he loses while playing, he needs to eat as much as 9,000 calories per day to gain it back and keep it."

Laken Tomlinson, A.J. Cann and Tre' Jackson may also hear their names called early in the proceedings.

Charles Krupa/Associated Press

Lost in the quarterback talk, wide receiver and edge-rusher hype and running back love fest is the fact that this center class is really good.

Cameron Erving saved the FSU line when he moved from left tackle to center, and his ability to play all over the line only adds to his versatility. Hroniss Grasu is ready-made for a zone scheme in the NFL and should start from day one.

You can say the same about run-blocking prodigy B.J. Finney. And don't sleep on Andy Gallik or Dillon Day—both are battle-tested and coming out of power conferences with a history of production.

Nick Wass/Associated Press

The defensive lineman position is loaded in 2015. Leonard Williams finds himself at the top of most draft boards, but Danny Shelton, Arik Armstead, Malcom Brown and Eddie Goldman could all realistically hear their names called in Round 1.

However, the talent doesn't end there. Teams can and will find productive players throughout the proceedings. Depending on how things shake out, we could see viable starters drafted much later than we're used to.

David J. Phillip/Associated Press

If you aren't familiar with the "edge defender" term, it's any defender who will line up outside the offensive tackle. That's a 4-3 defensive end or 3-4 outside linebacker, essentially. And you're going to hear a lot about this group, because it's absolutely loaded.

Dante Fowler, Shane Ray, Vic Beasley and Alvin "Bud" Dupree could all be selected in the top 10, and Randy Gregory would be in that group if not for a failed drug test at the combine.

The top-end talent is very, very good, and the depth is too. If your team doesn't get a blue-chipper at the top, you can steal Eli Harold in the late first or early second. Preston Smith and Owa Odighizuwa are big-bodied pass-rushers off the edge and natural fits in a 4-3 defense (something this draft lacks).

Mark J. Terrill/Associated Press

The line between inside and outside linebacker has been blurring in the NFL as of late, and with so many teams using both 3-4 and 4-3 looks, it has become necessary to simply rank linebackers as linebackers and do away with the Madden-esque "inside" and "outside" labels.

The 2015 class is good at linebacker, but not great. There's no Khalil Mack, Anthony Barr or C.J. Mosley here, so teams looking for a quick fix may have to settle. It's worth pointing out that many of the top linebackers are also undersized, with only Benardrick McKinney of the top five linebackers having ideal height and weight.

David Zalubowski/Associated Press

With offenses becoming more pass-oriented every year, we've seen the need for teams to draft and sign quality cornerbacks. Guys like Darrelle Revis and Richard Sherman are obvious examples, as we saw in last year's Super Bowl.

In 2015's draft, there are a number of tantalizing options available. 

Marcus Peters is the best of the bunch, but Ronald Darby, Trae Waynes, Kevin Johnson, Jalen Collins and Byron Jones could be Round 1 targets. UConn's Jones wowed us at the combine with his 12'3" broad jump and 44 ½-inch vertical. That type of athleticism is hard to pass up.

Matt York/Associated Press

The free safety position is not loaded this year, though there are still serviceable options with Gerod Holliman and Damarious Randall at the top.

Holliman has great instincts and hands, as you'd expect for someone with 14 interceptions in 2014. Randall, meanwhile, may be in play for the Dallas Cowboys at the end of Round 1, according to a team source.

Julio Cortez/Associated Press

Landon Collins looks like the cream of the crop at strong safety, though small-school prospect Jaquiski Tartt is an intriguing option early too.

Collins has a proven track record against some of the best schools in the country. We certainly can't say the same about Samford's Tartt, though here's what B/R's Matt Bowen saw: "It was the first day of workouts at the Senior Bowl in January, and a strong safety kept catching my attention. NFL body. Long. Aggressive. Playing fast. He was like a missile running to the ball."

"Must be a top prospect, right? Someone I'd heard of? Someone you'd heard of? Depends. Have you heard of Jaquiski Tartt?"

Julio Cortez/Associated Press

Rather than analyze kickers, punters and long snappers most people will have never heard of, I'd encourage you to read B/R's Mike Tanier's expertly crafted article titled "Kickers Are Prospects, Too: The Impossible Task of Scouting Kickers and Punters."