USC’s Marcus Johnson could be zeroing in on an NBA career

Watch Marcus Johnson, No. 0 in USC’s lineup, the one with the ear-to-ear smile.

And when the Trojans are fastbreaking, watch the rim: He’ll meet your eyes there, usually with a highlight slam.

But you won’t be alone. These days, the NBA is watching too.

“I hear from NBA guys all the time, scouts and GMs,” USC Coach Kevin O’Neill said recently. “But people are talking more about Marcus now than they ever have.”

Specifically, they’re talking defense, which the 6-foot-6 Johnson calls “his base” thanks to defense-minded coaches from high school through college. “I try to shut guys down,” he said.

Washington’s Quincy Pondexter was a victim: only two points on one-for-10 shooting against Johnson.

“He’s got great energy,” O’Neill said of Johnson. “He’s got great athletic ability. He’s strong. He’s got length.”

That shows on defense, but especially on his fastbreak dunks.

“I’m very athletic, and I love to dunk,” Johnson said.

Johnson knows people mostly see that side of him, but he’s working on that perception. He spends most of his days in the Galen Center shooting mid-range jumpers, and this past off-season ran on soft grass and beaches to improve his conditioning. Still, his offense (10.1 points a game) comes in spurts.

Against California on Thursday night, he capped a 25-0 USC run with five points of his own -- a mid-range jumper off a teammate’s steal, a free throw and then his own steal and another jumper.

“If he plays with high energy, our team plays with high energy,” O’Neill said. Added Dwight Lewis: “When he goes, we ride him.”

And USC wins. The Trojans are 25-12 when Johnson plays, largely because the fifth-year senior forward brings leadership to the inexperienced squad, which is evident during practice.

“He’s always telling me what to do in a nice way,” said sophomore forward Nikola Vucevic. “He’s always positive.”

Johnson’s ever-present grin is a dead giveaway of that. “I’ve got a lot to smile about,” he said.

He didn’t always.

Johnson spent two seasons at Connecticut, starting 24 games, before family issues brought him back to Los Angeles early in his junior season.

He picked USC as his new team, and picked jersey number zero because he wanted to start from scratch.

But he didn’t wear it much. He missed 11 games before becoming eligible after the transfer, and seven more because of a rotator cuff strain. He was granted a waiver for an extra season in May, but less than a week later, he announced he was going pro, only to change his mind later and give this season a chance.

Though it all, his mother, Chrissina, saw his frustration. “He wanted to be on the floor,” she said. “He wanted to be involved.”

She has attended every home game, except against Washington, which she missed because of car trouble. She cheers and sends text messages of encouragement, such as, “Winners deal with adversity.”

More adversity came this season, when the university imposed sanctions on the team for allegations surrounding former player O.J. Mayo, ending Johnson’s chance at a postseason.

When the news broke, Johnson told Chrissina, “None of us feel good about it.” That stuck with her, that he mentioned the team before himself, even now.

“Basketball is not an individual sport,” he said. “Tennis is, golf is. If you want to be an individual, go play one of those.”

Johnson is happy with basketball, and happy to be playing it here, in front of friends and family, with the California sun instead of Connecticut snow.

With the NBA watching now, he really does have a lot to smile about.

baxter.holmes@latimes.com