The battle to back up Philip Rivers begins during Chargers’ preseason opener

A hat instead of a helmet. Sneakers instead of cleats. A T-shirt and shorts instead of a jersey and pads.

Philip Rivers wasn’t in the uniform he surely wanted to be in — after all, this is a player who has made more consecutive regular-season starts than any active player in the league.

But the preseason isn’t about what you know. It’s about trying to find out what you don’t, and right now, the Chargers aren’t sure who would be next up if Rivers’ streak were to come to an untimely end.

The 15-year veteran quarterback was one of a handful of healthy scratches for the Chargers on Saturday night in their preseason-opening 24-17 loss to the Arizona Cardinals.

Cornerback Casey Hayward and wide receiver Keenan Allen also sat. Trevor Williams (ankle), receiver Travis Benjamin (shoulder) and defensive end Joey Bosa (foot) also weren’t available.

Rivers’ absence more than the others gave the Chargers coaches their first real look at the backup battle between Cardale Jones and Geno Smith.

Jones got the start Saturday and struggled, completing six of 12 passes for 50 yards while nearly being intercepted by former Charger Tre Boston. While he created more time with his feet and extended some plays, he also badly missed on some basic throws, including a swing pass that bounced at running back Melvin Gordon’s feet.

He led the Chargers on one scoring drive — aided by a defensive penalty — that ended with a 45-yard field goal by Caleb Sturgis.

Chargers quarterback Philip Rivers, right, watches warm ups with assistant coach Ken Whisenhunt on Saturday night.

(Rick Scuteri / Associated Press)

Smith took over for Jones right before the end of the half, and the Chargers moved into scoring position, but Sturgis missed from 41 yards.

Smith threw an interception in the third quarter on a deflected pass, then connected with Geremy Davis for a 47-yard touchdown.

Smith wound up completing 14 of 23 passes for 218 yards.

The Chargers’ final drive ended at the Arizona one-yard line when time ran out.

Smith and Jones figure to get the majority of the playing time again next weekend when the Chargers host Seattle on Saturday at StubHub Center.

Anthony Lynn said he would talk to his coaches and to veterans like Rivers to try to best manage their playing time in the preseason. Rivers played sparingly in the exhibition season last year, though he did appear for one series in the preseason opener.

Until the games count, Rivers probably will spend more time on the sidelines, with the Chargers trying their best to figure out their best option if the worst-case scenario occurs. And as of now, the best option remains keeping Rivers healthy.

Rosen debuts

Former UCLA quarterback Josh Rosen made his NFL debut, replacing Sam Bradford on the Cardinals’ second offensive possession.

The Chargers put Rosen under a lot of pressure, forcing the rookie into seven incompletions in 13 attempts, holding him to 41 yards on the six passes that were completed.

Former USC defensive end Uchenna Nwosu, who had said he was looking forward to giving Rosen a “hug,” nearly sacked him twice.

Okung protest

Chargers offensive tackle Russell Okung continued protesting social injustice and police brutality during the playing of the national anthem by raising his fistin the air. Okung made the same display during thenational anthem last season.

The protests, which began with Colin Kaepernick, have become a source of controversy in and around the league. with the NFL and its players unable to agree on a satisfactory policy, like allowing players to remain in the locker room before games.

After initially voting in favor of an anthem policy, the league agreed to suspend its implementation while trying to find a solution with the NFL Players Assn. in ongoing negotiations.

Etc.

Prior to Saturday’s game, the Cardinals held a moment of silence for Faye Spanos, the wife of Chargers owner Alex Spanos and mother of chairman Dean Spanos. She died last week at age 92. Funeral services will be held Friday in Stockton. The team played Saturday night with a decal on their helmets — her name written on a pink circular sticker. …Bosa, who didn’t play because of a foot injury suffered last week, didn’t make the trip. … Second-year safety Rayshawn Jenkins started alongside Jahleel Addae, while first-round pick Derwin James debuted with the second-string defense. …Undrafted rookieJJ Jones started the game as the team’s kick returner, an area the team is looking to improve this season. Jones returned one kick for 29 yards, setting up the Chargers’ first-quarter score.

dan.woike@latimes.com

Twitter: @DanWoikeSports