Klay Thompson of the Golden State Warriors knows that playing defense in the N.B.A. is difficult. As one of the league’s elite scorers, he causes his share of problems by launching 3-pointers from distant outposts. But he also has to spend about half his time trying to prevent opponents from doing the same.

“The game has become so spread out,” he said. “You’re out there on an island against these guys.”

Still, it is a challenge that Thompson has long embraced — and takes seriously. He is a connoisseur of basketball highlights on YouTube, not so much to pick up moves from opposing players but to figure out how to stop them. Whenever James Harden had one of his many big games for the Houston Rockets this season, Thompson plunged right into his clips.

“There are really no nights off as a defender,” Thompson said in a recent interview, “especially in the playoffs.”

Thompson, a 6-foot-7 shooting guard and a five-time All-Star, is getting tested again — with a sore right ankle, no less — as the Warriors take on the Rockets in their Western Conference semifinal series. But in helping Golden State to a 2-0 lead as the best-of-seven series shifts to Houston for Game 3 on Saturday, Thompson has played his familiar brand of rangy defense on guards like Chris Paul and Eric Gordon, collecting five steals while limiting his various assignments to 41.7 percent shooting.