Hype swirls for Sam Darnold, but the key to USC may be a bulked-up Ronald Jones II

USC’s offense zipped down the field against the starting defense on Tuesday for one of the first times in preseason camp. Occasionally, quarterback Sam Darnold struck with a long, vertical pass over the top. But most often, it was running back Ronald Jones II who pounded the Trojans’ front seven.

A troubling habit lingered in USC’s passing game. USC’s receivers weren’t always where Darnold wanted them to be.

“That would be a good observation,” coach Clay Helton said. “We’ve still got work to do. I don’t think we’re anything near a finished product.”

For all of the excitement surrounding Darnold, who remains the betting favorite to win the Heisman Trophy, USC’s offense early in the season could be built around someone else: Jones.

Jones enjoyed two of the best practices of his career on Saturday and Tuesday. He pummeled USC’s second-team defense in Saturday’s scrimmage. He slashed through the first team Tuesday. Helton called it possibly his best performance of the preseason.

Jones rushed for 1,082 yards and 12 touchdowns last season when he split time with Justin Davis. In three starts when Davis was hurt, Jones averaged 157 yards and three touchdowns.

Jones relied on his speed and elusiveness, but in the offseason he worked to add bulk. He did it, he said, with a combination of lifting weights and pounding fast food. Jones, a Texan, is a noted devotee of Whataburger, but he made do in Los Angeles with a slew of substitutes.

“The closest thing I found out here was Five Guys. That stuff smacks,” he said. “I ate a lot of Chipotle. I tried to cut out McDonald’s. It was hard. Popeyes a lot. Chick-fil-a.”

He ate, he said, “like four times a day. Big meals.”

The fast-food trips added 12 pounds. He now weighs 207, and he said he hasn’t lost speed. Helton said Jones’ touches in Saturday’s scrimmage were “powerful, powerful runs.” Jones said he won’t know “for sure for sure” how the weight will affect him until the first game, but he said he has added a new dimension to his game during practice.

“I’m breaking more tackles,” Jones said. “I get hit and I keep running, I’m like, ‘Oh, dang, I’m still up.’ ”

USC may rely on his durability early. Helton expects Darnold to make plays, but building chemistry with new receivers could take time. A rhythm has not yet formed during practice.

Helton cautioned that the sloppy routes seen Tuesday should clean up.

“Usually when you put in a new game plan, Tuesdays are when the most of my hair falls out and my blood pressure goes up because you’re putting in a little bit of the wrinkles that are new,” Helton said.

But Helton also said there would be growing pains. He has long advocated for a perfectly balanced offense. His ideal game, he said, would be 40 passes, 40 runs and at least 200 yards on the ground.

“That takes so much pressure off the quarterback,” Helton said.

Oh Captain

USC announced its team captains Monday night. There were no surprises but one rarity: The Trojans selected three defensive players and only one from the offense.

USC’s players selected Darnold, safety Chris Hawkins and linebackers Uchenna Nwosu and Cameron Smith.

Typically, Helton asks for two offensive names and two defensive names, but he said the votes overwhelmingly favored those four players.

Quick hits

Guard Viane Talamaivao left practice with a foot injury. He underwent precautionary X-rays, which revealed no fracture. Helton expects him to return within “a couple days.” . . . Tight end Daniel Imatorbhebhe, limited for most of the preseason by a hip flexor injury, participated in about half of practice Tuesday, including contact drills. . . . Safety Isaiah Pola-Mao separated his shoulder in Saturday’s scrimmage and will require season-ending surgery. . . . Linebacker Hunter Echols’ surgery to remove an infection in his hip was successful, Helton said. Echols could be sidelined for six to eight weeks. . . . Darnold was named a preseason All-American by the Associated Press. Smith and cornerback Iman Marshall were named to the second team. . . . USC will release its two-deep chart Sunday.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand