Finding value is one of the most important things during fantasy football drafts.

Value was even more important this year after a slew of injuries hit the running back position like a tidal wave. Only eight running backs out of the first 24 drafted running backs played the entire season, and just 17 of them eclipsed 10 games. Consequently, only 12 of the first 24 running backs this year finished the season as top-24 fantasy running backs.

Given the regular turnover at the top of the leaderboard, there presents an opportunity for us to find value picks and bargains. These players, who far outperform their Average Draft Position (ADP), provide an edge to fantasy owners who are able to find late-round gems.

Finding late-round values was crucial to cultivating fantasy success this year. We've already taken a look at the five biggest quarterback bargains of 2015, but who were this year's biggest bargains at the running back position?

In order to find this answer, I started with a baseline of digging through all MyFantasyLeague.com drafts that were done in mid-August or later. They were strictly 12-team PPR drafts and none of them were considered "mocks". From there, their final positional rankings were compared against their end of season finishing in point per reception (PPR) format. The net differences were found from where each running back was projected to start at the beginning of the season against their final end of season finishes.

5. David Johnson, Arizona Cardinals
Preseason ADP: RB47
End of Season Finish: RB8
Difference: +39

A favorite among #DraftTwitter, David Johnson finished the year with 13 total touchdowns to help skyrocket him up the fantasy leaderboards. Despite seeing limited snaps to start the season, Johnson finished his rookie year with 1,038 yards on offense on just 161 touches. He ended the season scoring the 8th-most fantasy points and the 16th-most fantasy points per game among running backs. Typically being drafted in the 12th round, the Northern Iowa product was a highly touted rookie who lived up to the billing.

Amid a crowded depth chart, Johnson was able to emerge as a viable fantasy threat. He finished the season with five different top-12 running back (RB1) performances and eight weeks with at least a top-24 (RB2) finish. Johnson didn't start seeing a majority of the running back snaps until Week 12 but showed the league -- and savvy fantasy owners -- that he was well worth the third-round draft pick Arizona spent on him.

Johnson finished the season with the second-best Rushing Net Expected Points (NEP) among running backs this year. Net Expected Points is numberFire's signature statistic that quantifies the number of points a player adds to his team versus how he's expected to perform, thus giving a true measure of efficiency.

Johnson had a modest rushing total of just 125 attempts but turned out to be one of the league's most efficient rushers. His Success Rate -- rushes that went for positive NEP -- ranked second among all running backs with at least 100 carries. David Johnson provided tremendous value for fantasy owners and should enter 2016 drafts as a potential top-10 back.

4. Jeremy Langford, Chicago Bears
Preseason ADP: RB71
End of Season Finish: RB29
Difference: +42

Another rookie makes our list as Chicago's Jeremy Langford provided substantial fantasy relief this season as long time veteran Matt Forte fought through injuries. Langford was often taken late in the 16th round or undrafted in some leagues but was able to provide a nice return on investment. He finished the season ranked 29th among all running backs in fantasy points yet a pedestrian 48th when looking at fantasy points per game. Langford played all 16 games this season but had his most value midway through the season where he scored five touchdowns between Week 9 and Week 12 without a healthy Forte.

During that four-week span, Langford racked up some very productive outings finishing as the RB4, RB1, RB19, and RB18 before Forte's Week 12 return. Unfortunately, Langford didn't have many more opportunities to seize fantasy stardom with Forte receiving the majority of the touches when healthy. However, the Bears looked to have their heir in waiting, as Langford was able to notch two elite top-six fantasy performances when provided the opportunity.

Langford was a very efficient running back when given his chances, ranking 12th in Rushing NEP and 11th in Success Rate. Forte ranked 14th and 3rd in the same metrics, as the Bears' offensive line deserves kudos for forming a sound rushing attack despite everything else going around the team. Chicago's rushing offense ended up ranking 13th in schedule-adjusted Rushing NEP, and Langford's rookie season should provide optimism for 2016 if the team decides to part way with Forte's expiring contract.

3. James Starks, Green Bay Packers
Preseason ADP: RB64
End of Season Finish: RB21
Difference: +43

It may seem like ages ago, but entering the season, Eddie Lacy was in the mix for being the first overall running back to be taken by some fantasy drafters. After watching James Starks look like the superior runner to Lacy in the playoffs, that notion seems like eons ago. The do-it-all 29-year old running back finished the year with 148 rushing attempts for 601 yards and caught 43 passes for 392 yards. Starks scored just five total touchdowns but was able to finish the season as the RB21. That was quite the climb for a running back who was typically drafted in the 15th round -- he rose 43 spots from his Preseason ADP. Starks finished as the RB35 from a fantasy points per game perspective.

Starks had a fairly productive season from a fantasy scoring view, though he was more of a boom-or-bust guy. He had seven games where he finished with at least RB2 production, but in three of those games, he was able to finish as a top-six running back. Starks evolved into more than just a handcuff this season, becoming a regular part of the running back rotation with Lacy starting only 12 games. Starks ended up leading the Packers in offensive snaps among running backs, outsnapping Lacy 46.0% to 41.0%.

A below average running back by our Rushing NEP metrics, Starks struggled consistently creating positive plays when given opportunities. The big play nature of Starks carried over from his fantasy production to his advanced metrics. Of the 44 running backs with at least 100 carries, Starks ranked 33rd in Rushing NEP, 40th in Success Rate, and 22nd in Total NEP -- which factors in both rushing and receiving. The 29-year old's contract is set to expire after this season, and the Packers might look towards the draft to supplement their running back woes if they're unwilling to endure another year of Starks' inconsistencies.

2. DeAngelo Williams, Pittsburgh Steelers
Preseason ADP: RB51
End of Season Finish: RB6
Difference: +45

When given the starting nod, DeAngelo Williams was a workhorse for the Steelers offense. After picking up 204 rushing yards and 3 touchdowns during the first two games of the season while Le'Veon Bell was suspended, Williams saw a brief hiatus in playing time until Bell's Week 8 injury. A preseason 13th-round draft pick, Williams returned tremendous value by finishing as the RB6 on the year. Williams also finished with an impressive RB14 ranking in fantasy points per game.

Williams was a fantastic producer from a weekly viewpoint, regularly producing usable fantasy weeks for owners. Williams finished with eight games ranking as an RB1 with five of those games finishing as a top-six running back for the week. Both of those counts were second-highest among all running backs, behind only Devonta Freeman. Excluding Week 17's injury-shortened game, Williams finished at least as an RB2 in every game he started without Bell.

From a numberFire metric view, Williams finished with the third-highest Rushing NEP and the seventh-highest Total NEP. He was able to combine both his fantasy success with metric-based success, making him one of this year's best fantasy bargains.

1. Theo Riddick, Detroit Lions
Preseason ADP: RB82
End of Season Finish: RB18
Difference: +64

This year's biggest bargain at the running back position ended up being Detroit's more surprising running back, Theo Riddick. The offseason hype train was at full speed regarding rookie Ameer Abdullah. Incumbent veteran Joique Bell was still around to garner touches. Another late-round draft darling in Zach Zenner was also receiving some heavy offseason buzz, ultimately leaving Riddick as the odd man out. Things changed rather quickly after Zenner was injured early, Bell quite presumably performed below average, and Abdullah inexplicably faltered, leaving Riddick to become a PPR monster for the Lions. Riddick was undrafted in the large majority of leagues (RB82) but finished as the RB18 on the season.

The 24-year old running back was a PPR nightmare for opposing defenses, catching 80 passes for 697 yards. Riddick was sprinkled in on runs here and there (only 43 attempts) but it was his receiving prowess that made him such a stud in PPR formats. He rarely saw high-end production on a given week -- just two weeks ranking inside the top-12 -- but routinely finished as an RB2 in eight different weeks. Only seven other running backs had more RB2 outings than Riddick.

Riddick had a terrible year by our Rushing NEP metrics, finishing 150th out of the 167 running backs to have a carry this season. However, his Reception NEP boosted his metric scores tremendously, with only Danny Woodhead having a higher score in this category. Collectively, Riddick finished fourth out of all running backs in Total NEP putting together a breakout year.

Honorable Mention: Top-Five Fantasy Points per Game Running Backs

There's always more than one way to view fantasy success, and end-of-season totals are just a small part of the pie. Looking at the game through a fantasy points per game lens, gives us a much different view of who some of the top running backs were this year when comparing them to their preseason ADP's.

You probably could've guessed it with nearly all of the end of season articles having to acknowledge his good play, but Devonta Freeman finished as the fifth-best bargain of the 2015 season in terms of fantasy points per game. Freeman was a fantasy workhorse, leading all running backs in top-6, top-12, and top-24 weeks after taking the starting spot in Week 3 and never looking back.

Karlos Williams was numberFire's top Rushing NEP champion and finished with the fourth-highest fantasy point per game differential. Williams often went in the 16th round of drafts (RB69) but finished as the RB30 thanks to six top-24 weeks. The aforementioned Theo Riddick finished the season ranked third in fantasy points per game, but I won't delve back into his success.

Dion Lewis was another early season fantasy darling, posting three weeks ranking as a top-6 back in just seven games played. Lewis was the second-best running back bargain in terms of fantasy points per game, far exceeding his preseason ADP. 

Injuries cut short Lance Dunbar's 2015 season, but he provided the best bargain on a fantasy points per game basis in PPR formats. With 21 receptions in his first three games, Dunbar was on pace for a breakout season for the Cowboys before a Week 4 injury derailed his season. Typically undrafted, Dunbar had a brief window to provide fantasy success before injuries ended his season, leaving him as an intriguing fantasy pick looking forward to 2016.