LOS ANGELES — Seconds passed, and USC basketball player Saint Thomas sat at the postgame podium on Sunday night still contemplating the question, unsure of how to answer because he didn’t have the answer himself. What’s not clicking defensively? “Um,” the forward said eventually, “I think that’s something that we’re still trying to figure out.” “Because it’s not like we’re a team that doesn’t play hard,” he continued. “And there’s no guy out there that’s, like, not in a puddle of sweat.” Indeed, and yet puddles of sweat paid no dividends in the Trojans’ 71-66 loss to Cal (3-1) on Sunday night – the first loss of Eric Musselman’s tenure – because of a clear early-season problem that has continued to plague this team. They might not quite be able to figure it out, yes. But most all are plain and well aware, as Thomas and point guard Desmond Claude and Musselman all admonished postgame, that USC (3-1) has a defense problem. It was overshadowed, early, by the shine of Musselman’s arrival and an unblemished record. On Wednesday, mid-major program UT Arlington dropped 95 points on the Trojans and shot 16 for 24 from 3-point range. Even in an explosive preseason exhibition victory over Gonzaga, as Thomas pointed out, USC gave up 93 points. And on Sunday, by the time guard Jovan Blacksher Jr. drained another 3-pointer at the end of the first half and big Rashaun Agee walked off the court yelling in frustration, the Trojans got shredded again to the tune of 42 first-half points by a Golden Bears team that shot well over 50% for most of the night. “Yeah, there’s some lack of lateral quickness that’s showing up,” Musselman said. “That’s why sometimes they make threes, because we’re too nervous to get too close because they’re going to go by us. And then when we crowd ’em, guys are going around us. “So, huge concern, but we gotta try to figure it out,” he continued. “This is a tough loss, for sure.” Especially tough, because the Trojans made necessary adjustments, an opportunity to close waiting at their fingertips. With 13 minutes left and USC continuing to struggle with pick-and-roll defense and any kind of interior presence, Musselman subbed Agee for starting guard Chibuzo Agbo Jr. – and gambled his hand at a purely small-ball lineup. Thomas, 6-foot-6 Claude, 6-7 guard Chibuzo Agbo Jr., 6-7 wing Terrance Williams II and 6-6 Swiss Army Knife Matt Knowling. Trailing by five, they provided an instant spark, Knowling swatting a late-clock Cal shot and freewheeling his way to a tip-in of his layup miss to cut Cal’s lead to one with nine minutes left. A couple of minutes later, Thomas scored back-to-back post-up buckets against Cal guard DJ Campbell, taunting him on subsequent trots down the floor with a rock-a-baby and a flex. And USC held Blacksher Jr., who had scored 18 first-half points, to one point on 0-for-3 shooting after halftime. “We kinda came back,” Thomas said of the small lineup, “and they couldn’t handle it.” But after that second Thomas baby-hook, USC’s offense went cold, going nearly five minutes without a bucket until a midrange by Claude cut Cal’s lead to 68-66 with 1:35 left. And the no-center gamble fell one play short, as Cal grabbed a backbreaking offensive rebound with less than 30 seconds left to set up virtual game-sealing free throws from Golden Bears wing Andrej Stojakovic (20 points). The Trojans missed nine of their final 10 field goal attempts as Cal scored eight of the game’s last 10 points. Musselman said it was a tough loss with USC coming up short in a matchup between two former Pac-12 rivals. Thomas admonished postgame that a roster made up mostly of transfers is still trying to figure out its defensive communication. “I think we showed the fans something, that we have energy,” said Thomas, who had 15 points. “I mean, we might have failed them, and lost. “But hey, we’re still here, and we still got something to prove.” NOTABLE Claude scored 13 of his 20 points in the first half, and Wesley Yates III scored all his 10 points before halftime. … Cal, now in the Atlantic Coast Conference, and the Trojans (Big Ten) played as nonconference opponents for the first time since 1921.