Every year, more than 250 players are drafted into the NFL.

It's a practice that predates media coverage, scouting departments and mock drafts, even if 1936's inaugural selection process took place in the same city -- the City of Brotherly Love -- that houses this year's grand event.

Every year, thousands of players are also passed over. Overlooked. Underrated. Left without a team.

But the story of undrafted rookies is increasingly of annual importance, if only because the pool of passed-over players continues to boast top-tier talent. Hitting on a rookie free agent, of course, is as unpredictable as striking gold in the draft, but history says not all undrafted talent should be ignored.

From record-holding kickers to Super Bowl-winning quarterbacks, here are the top 10 undrafted NFL players of all time:

10. Lou Groza

This man went straight from World War II to the Cleveland Browns. And as a recruit of the one and only Paul Brown, "The Toe" proceeded to set field-goal records, earn nine Pro Bowl trips and make a name for placekicking decades before the arrival of actual kicking specialists, all while helping Cleveland capture four championships. He was a generational special teamer, a Hall of Famer and forever celebrated by the Lou Groza Award, still issued annually to college football's top kicker.

9. Willie Brown

A staple of Oakland Raiders history whose defining moment may have been his age-37 pick six against Fran Tarkenton in Super Bowl XI, Brown was cast off by two teams before his career with the black and silver.

Willie Brown was a legend in the Oakland Raiders defensive backfield. USATSI

Signed and cut by the Houston Oilers in his rookie training camp and then traded from the Denver Broncos after four seasons, he retired as Oakland's all-time interceptions leader and still ranks in the NFL's top 25 in that category. A Hall of Famer, he also has three Super Bowls to his name.

8. Adam Vinatieri

He just keeps on kicking. Entering his age-45 season as the oldest active player in the NFL, he's racked up records in more than two decades of title-winning play. Responsible for game-winning field goals in two Super Bowls and a four-time champion overall, he's the only kicker to ever score more than 1,000 points with two different teams and also ranks atop the league's all-time list of postseason points scorers. It's a wonder he's only gone to three Pro Bowls between 10 seasons with the New England Patriots and another 11 with the Indianapolis Colts, but he's a lock for the Hall of Fame.

7. James Harrison

Like those of Vinatieri, some of his accolades are impressive just because of the age at which he claimed them. And unlike Vinatieri, Harrison is a linebacker.

James Harrison went from undrafted castoff to all-star pass rusher. USATSI

He'll be 39 by the time 2017 kicks off, and his journey began with quite a bit of overlooking. A three-time cut victim with the Pittsburgh Steelers from 2002-2003, he was on and off practice squads and even had a stint in the NFL Europe before embarking on a run as one of the league's feared pass rushers. Five Pro Bowls, a Defensive Player of the Year award and 79.5 sacks, a Steelers record, cement his legacy.

6. John Randle

When it comes to interior defensive linemen, you don't get much more productive than John Randle. His 137.5 career sacks are still good enough for 10th best in league history, behind only numbers from guys like Bruce Smith and Reggie White. Eight straight double-digit sack years helped him earn seven Pro Bowl trips, six All-Pro honors and a spot on the Minnesota Vikings' Ring of Honor. Into his mid-30s, he was still disrupting backfields with the Seattle Seahawks en route to a Hall of Fame induction.

5. Emlen Tunnell

Maybe the best player you never heard of, at least for the younger crowd, Tunnell made his mark on and off the field. Word has it that he hitchhiked from the Midwest to New York City in order to try out for the Giants, for whom he played starting in 1948. The first African American to suit up for N.Y. and, later, the first to join the Hall of Fame, his all-time interception total (79) still ranks as the second best in NFL history, behind only Paul Krause's 81. He was a nine-time all-star and 1950s All-Decade honoree.

4. Antonio Gates

The league's active leader in career touchdown catches, Gates abandoned a potential basketball career only to become one of the NFL's most prolific tight ends, not to mention one of the biggest football names of his generation.

Antonio Gates holds just about every Chargers receiving record. USATSI

The San Diego Chargers' all-time leader in just about every receiving category, he's long been Mr. Automatic, using five 900-yard seasons -- nearly 11,200 yards in all -- to earn eight Pro Bowl berths and a spot on the league's 2000s All-Decade Team. Hall of Fame, here he comes.

3. Warren Moon

Rejected not only at the draft but for more than half a decade afterward, the big-name signal-caller catapulted from Canadian Football League stardom to NFL turf, on which he gave inspiration to undrafted quarterbacks across the land. The first African-American QB to land in the Hall of Fame, he never brought home a Lombardi Trophy but found sustained success at the game's most important position with nine Pro Bowls, Offensive Player of the Year honors and two 4,000-yard seasons in an era with less emphasis on the aerial game. His signature No. 1 jersey is retired by the Tennessee Titans in honor of his Houston Oilers legacy.

2. Dick "Night Train" Lane

You don't know NFL history if you don't know "Night Train." Moon's success as a QB is hard to top, but to perennially dominate defensive backfields as Lane did for 14 years is a grand feat in itself. Even if you take away his inspirational backstory, in which he was abandoned as a child, went to junior college and served in the military, the Hall of Fame cornerback was a stud. His 14-interception rookie year has yet to be bested, his 68 total picks ranked second in the NFL when he retired, and his hard hits are immortalized through NFL Films.

1. Kurt Warner

Speaking of Hollywood backstories, Warner's transition from grocery store bagger and Arena League quarterback to Super Bowl MVP is about as familiar as the all-star resume that led to his impending Hall of Fame induction.

Kurt Warner went from grocery bagger to Super Bowl MVP. Getty Images

Cut by the Green Bay Packers as a rookie, the Iowa native went on to win a title with the St. Louis Rams' "Greatest Show on Turf" and contend for another as an aging vet with the Arizona Cardinals. His career passer rating is a top-10 mark in league history, many of his postseason passing marks rank first, and two MVPs made his 12-year NFL tenure an unforgettable one.

Honorable mention

To comb through the rest of the NFL's undrafted heroes is a tall task, but only because there is a plethora of other overlooked stars who warrant recognition. Among them, Brian Waters and Priest Holmes were staples of the Kansas City Chiefs offense, Rod Smith piled up 11,000 receiving yards for the Denver Broncos on the way to a Ring of Fame spot, Wes Welker became the NFL's first five-time 110-catch wideout despite a 5-9, 185-pound frame, and Joe "The Jet" Perry had back-to-back 1,000-yard seasons as a fullback and 1954 MVP.