TEMPE, Ariz. -- The Arizona Cardinals have figured out what their backfield will look like without David Johnson.

It’s crowded.

Kerwynn Williams will start Sunday’s game at the Indianapolis Colts, coach Bruce Arians said Wednesday. Williams will be backed up by Andre Ellington, who will be the Cardinals’ third-down back. Chris Johnson, who re-signed with Arizona on Tuesday, will “get some carries” as well.

That much is set. Arians said it’ll be hard to dress five running backs for games, which leaves Eli Penny and the newly acquired D.J. Foster vying for one active roster spot. Penny will likely be the fourth running back, Arians hinted.

“He had three [special-teams] tackles,” Arians said of Penny's efforts in the opener against the Lions. “So it’d be hard to put him on the bench.”

Having five running backs available might sound like a congested backfield, but Williams believes it gives all the backs an opportunity they haven’t had in the past, and provides the Cardinals with five different skill sets to utilize.

Arians said the Cardinals will have a featured back and go running-back-by-committee, all starting with Williams, who’ll also return kicks and punts Sunday.

“It’s definitely exciting,” Williams said. “It's an opportunity I haven’t had before. Definitely looking forward to it. I’m definitely excited for the opportunity.”

Sunday will be Williams’ first NFL start, and it will come against the team that drafted him in the seventh round in 2013.

Now, with his job status settled, he’s filling in for the most prolific running back in the NFL last season in Johnson, who led the league with 2,118 yards from scrimmage.

“All I can be is the best me,” Williams said.

But the 26-year-old believes he can deliver.

“I feel like you always got to be confident in yourself,” he said. “I think that’s the one thing that remains constant is your confidence in yourself. When things go wrong in your career or other people might see you in a certain way, I don’t feel like you can worry about that.

“I think the one thing that remains constant in my career is I’ve always been confident in myself.”

Chris Johnson’s role, meanwhile, wasn’t defined before he re-signed with Arizona, he said.

“I’m just trying to help the team win and wherever I can help, I can help,” the nine-year veteran said.

Foster, whom Arians “loved” coming out of Arizona State in 2016, will have a struggle ahead of him to be one of the four running backs active Sunday, but his versatility will help.

He began his Cardinals career Wednesday with a good first impression.

“He looked very, very good,” Arians said. “We loved him coming out of college because he can play slot receiver and he can play running back. He brings that added addition as a pass receiver. So just as he learns the offense, he gives us depth at that position.”

Arians has already observed that Foster is a quick learner. But while he digests the playbook, Foster’s best chance to get on the field Sunday -- or anytime soon, for that matter -- is on special teams.

“For me, it’s just come to work every day, learn as much as I can and be a sponge and just try to get the playbook as fast as I can," Foster said, "so I can get on the field and be a part of the team and help these guys.”