Caleb McLaughlin of ‘Stranger Things’ Slays Tennis Balls

Mr. Ristic had him practice a typical forehand swing and Mr. McLaughlin obliged, before politely revealing that he is in fact left-handed. Switching grips, he practiced again — drop and swing, drop and swing. Then Mr. Ristic moved to the backhand.

“Oh that’s beautiful,” Mr. Ristic said, praising his two-hand swing. “Perfect, awesome. You sure you need lessons?”

“You think I could become pro?” Mr. McLaughlin said.

“Definitely potential.”

Mr. Ristic had him face away, turning to hit the ball only when commanded. Then he fed him two balls at once. Then they practiced a few lobs.

“It’s a little like dancing,” Mr. McLaughlin said, reaching with a graceful extension of his arm. “It’s feeling good.” He hit the ball at the center of the racket, again and again, making the sound he loves: thwop, thwop, thwop.

He hadn’t had much training as a child, but even after so many years away, his natural athleticism brought the skills back quickly. He looked at ease and confident.

“I’m going to push you harder now,” Mr. Ristic said. “The better we do, the harder we go.”

On “Stranger Things,” Mr. McLaughlin’s character, Lucas, has faced trials more fearsome than two balls at once — demogorgons, mind flayers — with little more than a slingshot. (And, sure, OK, an ax.) “He’s experienced certain things that a lot of kids will never experience,” Mr. McLaughlin said meditatively. “There’s definitely a lot of trauma that plays in that.”