PITTSBURGH -- James Conner rivaled Tom Brady in jersey sales before playing an NFL snap. His courageous cancer fight resonated with fans on a human level. Those who understand what he overcame as a Pitt running back -- all those masked-up morning workouts between chemotherapy treatments for Hodgkin's lymphoma -- will celebrate his every tote of the rock.

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But Conner's journey as a first-year Steeler was a common one for many rookies: He showed flashes in 2017 but generally struggled with the nuances of the professional game. That's why Conner wasn't about to pump his fist over a few swift cuts in the open field during Thursday's organized team activities, which featured Conner prominently in the absence of Le'Veon Bell.

Out here, it's simply limiting mental errors and earning the trust of coaches and teammates, who will watch closely.

"Didn't really do much [last season] so I have a lot to prove," Conner said. "I just needed to learn more, needed to grow more. I'm in the process of growing right now."

It's no coincidence that quarterback Ben Roethlisberger, unprompted, brought up Conner when asked about Bell. This is a "big time" for Conner, he said, to get reps "so we can all see what he can do." Wide receiver Darrius Heyward-Bey said virtually the same thing when asked about Bell.

A spotlight is squarely on Conner's shoulder pads in Year 2.

James Conner has a chance to show the Steelers what he can do in his second season with Le'Veon Bell sitting out offseason workouts. Keith Srakocic/AP Photo

Gaining 144 yards on 32 carries last season was enough to showcase Conner's potential, but a Week 15 medial collateral ligament tear cut his production short. Conner is happy to be healthy, which makes him an intriguing backfield option alongside rookie Jaylen Samuels and veterans Stevan Ridley and Fitz Toussaint. There's depth and competition behind Bell, and Conner needs to shine.

Tight end Jesse James believes Conner will do just that, assuming he overcomes a few rookie pitfalls he noticed -- in the film room and on the field.

"He's a little bit more confident in the playbook, handling protections -- he's just in better shape," James said. "He's running fast, running every ball to the end zone. He looks good."

James knows every rookie who steps foot into the UPMC Rooney Sports Complex learns quickly his conditioning needs to improve. James came here three years ago as a 272-pound tight end out of Penn State and stands 252 today. Today's NFL game is all about speed, so keep up.

Even with that hurdle, Conner was always a punishing runner, which the Steelers covet. The details were a problem, though. Former offensive coordinator Todd Haley pointed out lackluster special-teams play kept Conner out of the rotation.

James said fine-tuning pass protections should catalyze Conner's second season.

"If he makes a jump there, we'll see huge improvements," James said. "He'll make a big jump this year."

To validate that faith, Conner is taking nothing for granted.

He plans to improve in "every category," he said, citing route-running and a full command of the playbook.

Bell will be the workhorse upon his return, but Conner wants to punctuate his NFL career sooner than later.

"I haven't proved anything yet," Conner said. "Just another opportunity for me to prove to my coaches and earn respect from my teammates that I'm capable of playing on Sundays."