Column: Old roommates to face off in Chargers-Raiders game

Down to their fourth tailback, the San Diego Chargers should have pylons and flashing signs surrounding their running game under repair.

It’s only fitting, then, that rookie Branden Oliver should step into the fray, a guy who wore a hard hat in college. Really, he did.

Oliver’s work ethic was legendary at the University of Buffalo, so much so that his coach gave him a royal blue construction hat that the diminutive running back wore proudly on every road trip. He was never sheepish about donning it on the team bus, in airports, hotels, wherever.

Last Sunday, the undrafted Oliver was a jackhammer, scoring two touchdowns in a 31-0 blanking of the New York Jets and doing it in roll-up-the-sleeves style with 114 yards rushing and 68 yards receiving. He looked like a hologram of former Chargers lightning bug Darren Sproles, same No. 43 and all.

For Oliver, who went by the first name “Bo” in Buffalo because of his initials, there’s a personal twist to Sunday’s game at Oakland. He’ll be going up against his best friend and college roommate, linebacker Khalil Mack, the fifth overall pick. They made their recruiting trip on the same weekend to Buffalo, astoundingly the only school to offer either of them scholarships.

“It was a pretty unique situation, man,” Mack said by phone Thursday. “Speaks to why we hung around each other so much. We both had that same hunger, and we’ve still got it now.”

That Mack is starting for the Raiders is no surprise; it would be a stunner if they didn’t have their top pick on the field. But who could have predicted Oliver would be bringing Chargers fans to their feet, particularly this early in the season?

Injuries to running backs Ryan Mathews, Danny Woodhead and Donald Brown got Oliver onto the field. If Oliver has another performance like the one he had last Sunday, it would be difficult to imagine the Chargers taking him off it.

Generously listed at 5 feet 8, the 208-pound Oliver has the tree-stump thickness of Raiders running back Maurice Jones-Drew, not the slighter build of Sproles, now with Philadelphia.

“He reminds me of [Jones-Drew] in a lot of different ways,” Mack said. “Maurice, you can’t see him when he gets behind one of those linemen. Bo was like that my whole career.”

Oliver certainly isn’t invisible now.

Among the other out-of-the-blue performers in the first five weeks:

Austin Davis, QB, St. Louis: Although the Rams are 1-3, Davis has the most spectacularly improbable story of the season so far.

He was a walk-on at Southern Mississippi, wound up playing four years and breaking most of Brett Favre’s passing records. He went undrafted in 2012 — at least by the NFL — but was selected in the 32nd round of the baseball draft by the Boston Red Sox.

He was signed, then cut by the Rams, then spent most of the 2012 season on Miami’s practice squad. The Dolphins eventually cut him too, and Davis briefly worked as a volunteer football coach at Westminster Christian Academy in suburban St. Louis. The Rams circled back and re-signed him after starting quarterback Sam Bradford suffered a season-ending knee injury last October.

Two months ago, Davis was the Rams’ fourth-string quarterback, and it looked as if he probably wouldn’t make the final roster. Because of injuries and opportunities, though, he moved up the ranks and recently was named the starter for the rest of the season.

He has been a bright spot for St. Louis, completing 67.8% of his passes for 1,129 yards, with a respectable passer rating of 96.8, 10th among regular starters and better than Matt Ryan, Eli Manning, Jay Cutler, Drew Brees and others.

Seantrel Henderson, RT, Buffalo: Because of marijuana issues at the University of Miami, Henderson tumbled all the way to the seventh round in last spring’s draft, a far cry from his days as one of the country’s most heavily recruited high school standouts. He was a find for the Bills, though, and since has locked down the starting job at right tackle.

So far, he has been a dream for the Bills, whose line could have been reeling in light of the disappointment of second-round tackle Cyrus Kouandjio, who has yet to dress for a game, and left guard Chris Williams, a free agent who has battled back issues since the summer.

Chandler Catanzaro, K, Arizona: An undrafted rookie out of Clemson, Catanzaro has been perfect so far, making 11 field goal attempts, a franchise rookie record. He earned the job after winning a training camp battle with veteran incumbent Jay Feely.

Despite kicking off just five times in college, Catanzaro has caught on quickly and has 14 touchbacks in 22 kickoffs for a rate of 63.6%, better than half the kickers in the league. So far this season, the best opponent starting position following a kickoff is its 22-yard line.

Allen Hurns, WR, Jacksonville: Hurns, an undrafted rookie, has come back to earth after his spectacular debut in the first quarter of Jacksonville’s opener against Philadelphia — two catches, both for touchdowns. He scored once more, in Week 3 against Indianapolis, and now has 16 catches for 280 yards. He struggled against Pittsburgh last Sunday, with three drops and a holding penalty, so he’ll be looking to redeem himself in Week 6 at Tennessee.

Andre Williams, RB, New York Giants: Williams was a fourth-round pick out of Boston College and a Heisman Trophy finalist, so that largely disqualifies him as an out-of-the-blue performer. But he deserves mention because he figures to shoulder a lot of the load Sunday night in a pivotal NFC East game against Philadelphia.

When Rashad Jennings went down with a knee injury in the third quarter against Atlanta on Sunday, the bruising Williams stepped in and did some damage. He bashed his way to 65 yards in 20 carries, caught a couple of passes, and scored a key touchdown in the 30-20 comeback victory.

Larry Donnell, TE, Giants: Undrafted in 2012, Donnell spent his rookie season on the practice squad, and played mostly on special teams last season. He broke out this season with 25 catches in the first four games, including a forehead-slapping performance in a 45-14 rout of Washington — seven catches, three for touchdowns.

Everybody was surprised by that, even Donnell.

Proof: He had benched himself on his own fantasy team.

sam.farmer@latimes.com

Twitter: @LATimesfarmer