PITTSBURGH -- Wearing a pair of boxers and matching socks covered in flame emojis, JuJu Smith-Schuster is frozen in a running motion beside a Pittsburgh highway, his arms pumping and knees high.

Against a gray backdrop, the baby blue billboard displaying his collaboration with MeUndies pops.

Like his advertisement, the Pittsburgh Steelers wide receiver stands out as an enigma in a gritty town -- a budding superstar for the next generation playing for an old-school, hard-nosed franchise. In the first two years after he was selected in the second round of the 2017 draft, the 23-year-old receiver made a name for himself as the fun-loving sidekick to Antonio Brown.

"[Smith-Schuster's] a high-energy guy," Steelers coach Mike Tomlin said. "He brings energy to his work. He's jovial at times. That's been him since Day 1 when we drafted him a number of years ago."

But fandom can be fickle and as the offense struggled in Smith-Schuster's first year as the No. 1 receiver after the Steelers moved on from Brown, public perception of the young receiver started to shift. Smith-Schuster was criticized for doing things in line with his big-kid persona -- like partying on stage with his favorite YouTuber, just hours after the Steelers' loss to the Seattle Seahawks, and broadcasting it all live on Instagram. Later, he took heat for posting a video that appeared to show him speeding more than 100 mph in his BMW less than two weeks after being diagnosed with a concussion.

Hindered by injuries and instability at quarterback after an elbow injury sidelined Ben Roethlisberger for most of the season, Smith-Schuster's on-field production dipped dramatically. Missing four games, Smith-Schuster finished his third year in the NFL with 552 receiving yards and three touchdowns -- a fraction of his 1,426 yard, seven touchdown 2018 season. He had one 100-yard receiving game.

With so many obstacles, Smith-Schuster wasn't having as much fun. And those closest to him could feel the change.

"He was definitely going through a lot," his mom, Sammy Schuster, said. "He was calling me more, we were talking more. I was kind of worried about him. This is a guy who, this is his passion. It just seemed like it was one thing after another."

But after a tumultuous season, Smith-Schuster is ready to rebound. Entering the final year of his rookie deal, he is playing for his future with a Pittsburgh organization facing difficult decisions after the season. Or he's giving a last audition for the other 31 teams before free agency.

And perhaps even more importantly, he's ready to have fun again.

In a wide receiver room of young, versatile talent, how does Smith-Schuster view himself?

The leader? The deep threat? The slot? The X?

The answer is simpler than that: He's the fun one.

"I am definitely the guy that is trying to make everyone laugh and enjoy their job," Smith-Schuster said. "Making the best out of it. I think there are days where we are tired or we are down and feel like we just don't want to do it, but I am the guy that comes in and says, "Let's go, man. Let's have fun today, make the most out of it.' Like I said, we are always lit."

"He was definitely going through a lot. He was calling me more, we were talking more. I was kind of worried about him. This is a guy who, this is his passion. It just seemed like it was one thing after another." Sammy Schuster, JuJu's mom

It's true, fun is his trademark. Earlier this year he filed paperwork to trademark his catchphrase, "It's Litty." And it was the inspiration for the flame emoji design on his MeUndies collaboration.

"It's always lit with him," said offensive lineman Zach Banner, who first met Smith-Schuster at USC. "It's always fun. ... he has standards for himself and he has dreams and he has goals. It might be a Trojan thing."

The carefree, big-kid mentality comes from growing up in a big family. Born John Smith, the second-oldest of seven makes a point of spending time with his siblings.

In college, he'd come home and play Barbies with his younger sister. Now, the two make TikToks. Smith-Schuster also sent a gaming system to his 15-year-old brother so they can play online, and he plays Fortnite with his 9-year-old brother.

"He's a big kid when he comes home," Sammy said. "That's what I love about him. Once he opens that door and he's in this house, it's like everything else doesn't matter. He's not this big football player guy. He's just John the older brother that these kids look up to."

Smith-Schuster became a fan favorite as a rookie when he rode his bike to Steelers practice and had it stolen. Since then, he's built a brand around being fun and living every Gen Zer's dream: playing video games, speeding around in cool cars like his Polaris Slingshot, and going viral on social media with his dog Boujee.

But last year wasn't fun.

A season that started with the death of wide receivers coach Darryl Drake felt like it got more challenging by the week. There was Roethlisberger's injury, then backup quarterback Mason Rudolph's concussion. A couple weeks later, Smith-Schuster sustained a concussion and a knee injury in a loss to Cleveland, overshadowed by the game-ending brawl between Browns defensive end Myles Garrett and Rudolph.

With the passing of Drake, Smith-Schuster lost one of his closest confidants and a mentor in the Steelers organization.

"It's not just when I was hurt, but even during the season, certain situations that we were dealing with, I wish I had time to talk to him," Smith-Schuster said. "I prayed, long nights that I hope he answered my prayers.

"We always talked about life, whether it's family, friends, money. Anything you can think of, we always talked about it. Because at the end of the day, football will only last so long. It's what lasts after is the stuff that we talked about."

Tomlin filled some of the void left behind by Drake's death, talking with Smith-Schuster when he needed it, but something was still missing.

"[It's] the normal maturation of a player who is extremely talented and had a lot of early success and at times faced the natural adversity that the game of football presents," Tomlin said. "Be it injury or injury to those around you. Or the attention that comes with being a quality player. JuJu is very experienced, but he is a relatively young guy. He was 20 when we drafted him. It is my job to assist him in natural growth and maturation, and that is an element of the job that I embrace."

Sammy Schuster was 3,000 miles away, but she could tell something was wrong with her oldest son.

Normally the carefree guy with the thousand-watt smile shouting his trademark-pending slogan, Smith-Schuster was withdrawn.

"I'm in California," Sammy said. "I can't be there for him. I can't hug him, I can't look at him and hug and tell him everything is going to be OK. So I relied on our conversations and just sent him text messages almost every other day to tell him, keep your head up and keep encouraging him. ... Then it kind of got to the point where when I was texting him, he wasn't texting back. I'm like, ‘What's going on with him? He usually texts me back.'

"There was just something inside of my gut, we just have to fly out there."

When Smith-Schuster got back from practice before the Steelers' game against the Buffalo Bills in Week 15, Sammy and Lawrence, Smith-Schuster's stepdad, were sitting in his apartment. Startled, he grinned and hugged them.

He played it off, but Sammy could read her son. He needed this.

They talked for hours that night as Sammy updated Smith-Schuster on their family. They didn't mention football once.

"I could tell just by the look on his face that he was so happy that we were there," Sammy said. "He hugged his dad, hugged me, and we just sat there and we just talked."

Later that weekend, they went to the Steelers' Sunday night game. It didn't matter that Smith-Schuster's knee injury kept him from playing. She just wanted to be there for him.

It was a disappointing season by nearly every measure, and at the worst time.

Following their usual timeline, the Steelers could start negotiating an extension with Smith-Schuster following the 2019 regular season.

But after last season it was hard to justify a monster deal, especially with so many other expensive contracts on the books. With a week left until the Steelers' window for contracts and extensions unofficially closes with the start of the regular season, it seems increasingly likely that Smith-Schuster plays on the last year of his rookie deal.

But that's OK with him.

"I'm not worried about that," Smith-Schuster said during camp. "With everything going on right now, you just never know what could happen. As for me, I'd love to be a Steeler, but at the end of the day, I'm here to play ball, win games for the team and for the organization."

Fully healed from the knee injury, Smith-Schuster spent his offseason preparing for a make-or-break year, and Sammy began noticing a shift in her son's demeanor.

Before a stop in Miami to host the JuJu Bowl -- a Madden tournament live-streamed with Caffeine, a social broadcasting platform, in front of an audience -- he began working out with celebrity trainer Corey Calliet in one-on-one sessions in Calliet's garage-turned-gym. Smith-Schuster posted videos of his training on Instagram, for a while replacing his usual feed of gaming videos.

He bought his family a house in Yorba Linda, California, made plans to put money back for his siblings' college funds and launched the underwear collaboration.

When he came back to Pittsburgh, he spent time riding jet skis on the rivers and shooting off fireworks on top of a parking deck during the Fourth of July weekend.

And even more importantly, he's having fun again on the field. With Roethlisberger back, Smith-Schuster is starting to look more like the receiver who earned a Pro Bowl nod in 2018 as the pair rekindle their chemistry.

"We all know JuJu is a playmaker," wide receivers coach Ike Hilliard said. "We all know that he is going to be a guy we get the ball to to jumpstart our offense in a big way. And he's looking forward to being JuJu."

Recently in training camp practice, as Roethlisberger pump-faked, Smith-Schuster got open and caught a pass from down the seam on a post route. Days later, he snagged a touchdown pass near the goal post in Friday night's scrimmage and celebrated by spinning the ball in the end zone grass.

"He's definitely back to being his old self," Sammy said. "He's excited about the new wide receivers that are coming in. I was talking to him after the first practice, and I said, ‘How's everything going?' He was like, ‘Man, I'm so happy Ben is back. Everybody, our team, we're ready to go.'

"I think he's back."