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There was a reason the San Diego Chargers gave Donald Brown a $10.4 million contract to be their third-string running back.

When lead back Ryan Mathews went down with an MCL sprain in the Chargers' Week 2 win over the Seattle Seahawks, Brown got the call to replace him as the team's featured back and between-the-tackles complement to receiving back Danny Woodhead.

This should be how the team operates until Mathews returns in four or five weeks—use Brown as a jack-of-all-trades back while Woodhead keeps his current role.

The Chargers will either sink or swim with Brown's upgraded status. He is now their most important component, a running back on a run-heavy team that wants to milk the clock with inside runs, quick passes to backs and a heavy serving of Antonio Gates.

As long as Mathews is out, Brown is the Chargers' X-factor. Luckily for San Diego, Brown shines when given the opportunity—did you know Brown was one of the best running backs in the NFL last year?

Football Outsiders ranked Brown second in both DVOA and success rate in 2013, meaning he was the second-best running back relative to the defenses he faced and the situations his offense placed him in.

Brown's limited sample size likely bumped him up in the rankings, as he finished the season with 537 yards rushing on 5.3 yards per carry. With a Marshawn Lynch-like workload, his rushing average wouldn't have been as appealing.

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But keep in mind that Brown did all of his work behind one of the league's weakest offensive lines—the Colts ranked 15th in adjusted-line yards compared to the Chargers’ third-place finish in Football Outsiders' 2013 offensive line rankings. However, the Colts finished 21st in open field yardage rate while the Chargers finished 27th.

Translation: Brown played better behind a poorer offensive line last year than Mathews did with one of the league's best offensive lines.

However, Brown and Mathews did play different roles last season, and Brown (5'10", 207 pounds) might not be as accustomed to taking the pounding that sledgehammering Mathews (6'0", 220 pounds) did on a team that doesn't need to engineer as many pass-heavy comebacks as Indianapolis needs.

That's why Brown can't just be Mathews' direct replacement. The Chargers must keep his strengths and weaknesses in mind—they were planning on a three-headed monster at running back, after all. Brown isn't Mathews and Branden Oliver isn't Brown. If the Chargers do not tweak their game plan, the running game will worsen.

Brown can block and catch, but he doesn't particularly excel at either. He is best as a pure runner out in space—in the open field he is dangerous, but there are games in which he can't get the necessary yardage in close quarters, something Mathews excels at. This was evident throughout 2013, when Brown averaged between 3.5 and 5.5 yards per carry just three times, according to Jason Peters of SBNation. That is the very definition of boom or bust.

Brown's extreme game-to-game differentials were due to three factors: a limited number of carries per game, his inconsistent vision as a ball-carrier and the Colts' talent-deprived offensive line.

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Yet when he's on, he's on. Check out this 51-yard touchdown run Brown had versus a stout Kansas City Chiefs defense last year.

Brown is one of the NFL's best at breaking arm tackles. If the Chargers can consistently get him out in the open field, the running game should pick up right where Mathews left off.

But can the Chargers adjust to Brown's talents?

They haven't so far. Brown has nine carries for 19 yards this season, and one of those carries was a 16-yard run versus the Seahawks. Subtract that, and he is averaging an appalling .33 yards per carry. This is especially concerning when factoring in Brown's role as a change-of-pace back the first two weeks, which should lend itself to a higher rushing average.

Brown's poor production stems more from the Chargers' difficult matchups than Trent Richardson-like ineffectiveness—the Cardinals and Seahawks were two of the NFL's best run defenses last season, and they look to be just as formidable in 2014. Upcoming games against the Buffalo Bills and Jacksonville Jaguars should boost his numbers.

The situations Brown has ran in isn't exactly advantageous for a runner, either—Brown has carried the ball seven times on first down and twice on second down this season, and several of these runs were when the Chargers were milking the clock against Seattle. Give him more third down work when the defense isn't peeking into the backfield, and he will look much better with more room to operate.

And that's how Colts offensive coordinator Pep Hamilton used Brown in 2013—extensive third down usage along with frequent draw plays and traps. Hamilton has gotten plenty of flak in his first two seasons with the Colts, but he certainly used Brown well in 2013. Brown glides as a runner, and at top speed he can shed tackles and make some nifty moves. Along with two-tight end sets, Hamilton played to these strengths with two running plays: the draw and the trap.

Pro Football Focus

Play designs, like the draw and the trap, designed to get Brown through the interior at full speed were some of Indianapolis' most efficient running plays last year. Per Pro Football Focus (subscription required), he averaged 7.0 yards per carry on running plays between the guards in 2013 for a total of 198 yards and seven missed tackles.

San Diego can easily do what the Colts did with Brown, as the Chargers frequently employ draw plays in their offense and used them to their advantage against Seattle.

When used correctly—and with not as much frequency as Ken Whisenhunt did last season—the draw play can be a very effective wrinkle in a Chargers offense that took 92 percent of its snaps in the shotgun formation last year, according to Pro Football Focus. Defenses are used to the Chargers setting up in the shotgun and want to tee off on their now-vulnerable interior line. When pass-rushers get too aggressive and too far upfield in their attempts to sack Rivers, Brown can run right through the massive lanes created.

Brown still will need to work traditional power running plays in lieu of Mathews, and that's where center Rich Ohrnberger and right guard Johnnie Troutman could really be exposed as the season goes along. Mathews himself wasn't doing much behind that combination, averaging just over three yards per carry in two games.

The 27-year-old Brown didn't have a great offensive line situation in Indianapolis, and it's not an area of strength for San Diego, either. He'll have to put faith in reliable run-blockers King Dunlap and D.J. Fluker at left and right tackle, respectively.

Brown now gets to show the NFL why San Diego paid a surprising amount for his services. As talented as Mathews is, he has bad luck with injuries, and the Chargers logically didn’t want their offense to sputter if Mathews went down.

What San Diego did in its Week 2 upset of Seattle was dominate time of possession, chipping away with inside runs, draws and short passes until the Seahawks wilted under the San Diego sun. With Brown in place of Mathews, the Chargers can still execute this philosophy and win games—they just need to cater to Brown's strengths without abandoning their offensive identity.