Running back David Johnson carries the ball against the Chargers.

Andre Ellington put on a show in the first preseason game, and it was David Johnson's turn Saturday against the Chargers. While Chris Johnson has yet to make his Cardinals debut, his whole career has been a long highlight reel.

With their combination of speed and pass-catching ability, the trio of running backs seems poised to turn heads out of the backfield this year. And while that dazzle is a welcome sight, the group can only truly succeed if they master

the grunt-work as well.

That includes getting the job done in obvious running situations, like on third-and-short or near the goal-line, something the Cardinals struggled with at times last season. The 224-pound David Johnson showed positive signs in his 13-carry, 66-yard debut against the Chargers, using stiff-arms and strength to fight for yards after contact.

Coach Bruce Arians wasn't ready to anoint him the short-yardage back – Chris Johnson seems to have the edge at this point based on experience – but David Johnson feels he's here for that reason.

"With my ability and my size, I need to be able to be that downhill runner," David Johnson said.

A weak area for the running backs on Saturday was pass protection, a facet which may not be as exciting as a big run but is just as important. The Cardinals allowed six sacks in the first half to the Chargers, and at least a pair of them seemed to be attributed to Ellington and Johnson not picking up blitzes.

Arians said it's a common problem for young running backs. They leave college knowing one or two protection schemes and need to learn 14 or 15 in the NFL.

"That's the heaviest load for a back," Arians said. "They come in and they know how to run, and they know how to catch, most of them. The pass protection schemes can overload them really quick."

MORE FRIENDLY FIRE FROM BUCANNON

Defensive end Calais Campbell grabbed a microphone and directed a question at safety Deone Bucannon during an interview session after Monday's practice. On Saturday, Bucannon accidentally hurtled into Campbell in the first

quarter, knocking the star defensive end out for a play.

Campbell returned quickly – resulting in a sigh of relief for Cards fans -- but he wanted to know if Bucannon felt bad about it.

"I definitely did," Bucannon said. "If you see after the play, I had my hands on my head, like, 'This is our top guy!'"

It was the second time in his two seasons Bucannon injured a star defensive teammate, following a collision which knocked cornerback Patrick Peterson from the Eagles game last year with a head injury.

"I was like, 'Oh my gosh, here we go again,'" Bucannon told Campbell. "I was really just hoping and praying you weren't hurt."

HAMSTRING STRAIN KEEPS JERRAUD POWERS OUT

Cornerback Jerraud Powers returned to practice last week after missing the preseason opener with an oblique injury, but subsequently injured his hamstring strain and missed the Chargers game. Arians said Powers will be shut down for a little while to make sure it heals up.

Linebacker Sean Weatherspoon (hamstring) is still sidelined and isn't expected back until the end of this week at the earliest. Wide receiver Michael Floyd (hand) and guard Mike Iupati (knee) are still out indefinitely, but there was some good news for Chris Johnson (hamstring) as he's been upgraded to day-to-day. Tight end Jermaine Gresham (back), wide receiver Brittan Golden (shoulder) and guard Earl Watford (ankle) sat out Monday but are expected back Wednesday following the team's day off.

Linebacker Shaq Riddick made his training camp debut on Monday after missing nearly all of the offseason with a hamstring injury but was limited. Tackle Rob Crisp (knee) and cornerback Jonte Green (hamstring) also returned to practice.