LOS ANGELES — Arizona’s effort on defense recently has been nothing short of lackadaisical.

The Wildcats’ inability to stop their opponent, especially considering their top-notch defensive play for the early portion of the season, is confusing.

Head coach Sean Miller is baffled as well.

“We’ve practiced 81 times,” Miller said after Wednesday’s 89-78 loss to USC. “Played 28 games. 81 times, 28 games. We’ve been to the Bahamas in terms of our foreign trip; that’s an additional 14.

“And we couldn’t rotate on a side ball screen.”

They didn’t do much else right on defense, either.

Sophomore guard Nick Johnson, Arizona’s supposed “defensive stopper,” was a non-factor.

The 11th-ranked Wildcats (23-5, 11-5 Pac-12) didn’t box out; USC drove to the basket with ease and made its (frequently open) shots. The Trojans made some off-balance circus shots too, but anomalies like that are to be expected over the course of a game.

The Trojans’ 89 points were a season-worst for the Wildcats, and USC shot 61.1 percent from the field, 60 percent from three, and 81 percent on free throws and outrebounded the Wildcats 34-29. USC turned the ball over 17 times, but shooting efficiency at that rate negates coughing the ball up.

If the Wildcats are going to bounce back against UCLA (21-7, 11-4) on Saturday at Pauley Pavilion, against a team with significantly better offensive firepower than USC, it will take an improvement in, at minimum, defensive effort.

“Effort is one thing every person has got to put into the game,” said freshman forward Grant Jerrett, who had 10 points, three rebounds and two blocks against USC. “And we picked and chose when we did it tonight, and that’s why we lost.”

Effort, Miller said, isn’t something that can be turned on and off at this point in the season.

“You have to be extremely talented to pick and choose how hard you play,” Miller said, “and we’re not. What makes us a good team is when we’re clicking on all cylinders on both sides of the ball and when our depth takes hold.”

In their last game against the Bruins, on Jan. 24 in McKale Center, the Wildcats fell into a quick 21-5 hole, which couldn’t be fixed by a late comeback attempt and resulted in their 11-point loss.

If you leave Shabazz Muhammad open, he won’t miss.

If you leave Jordan Adams open, he won’t miss.

If you leave Travis Wear open, he won’t miss.

“We’re faced with an immense challenge on Saturday,” Miller said, “and if we don’t play harder on defense — better on defense — I don’t think the game will be close.”

The last time it played against the Bruins, Arizona was ranked No. 6. In the last six games, it has looked more like the sixth-best team in the conference.

Overall, Miller has called this his best defensive team at Arizona.

“But recently, this is the worst defensive team I have ever coached,” he said.

In their last six games, the Wildcats are 3-3. They’ve allowed 68.1 points per game at a 46.9 percent clip.

Excluding the Washington and Washington State blowout wins, that number jumps up to 75.25 points per game and 52.4 percent, respectively.

In games since Nov. 20, when the Wildcats gave up 70 or more points, they are 2-5.

“I’m very frustrated with the situation,” said senior forward Solomon Hill. “You want everybody to play a certain way and accept a certain standard being on the court, and it’s just not that case.”

Hill certainly wasn’t at fault for Wednesday’s loss, and neither was forward Kevin Parrom.

With effort lacking elsewhere, both seniors stepped up.

They had a combined 37 points on 50 percent shooting (13-of-26) and Hill had six assists, three rebounds and five steals.

“Kevin Parrom and Solomon Hill really showed up,” Miller said. “Without them, I don’t know where we would’ve been tonight.”

Miller wasn’t really pointing fingers at the freshmen, either, because they are freshmen.

“I’m disappointed in my teammates,” Parrom said. “I’m just disappointed. We had some guys — not that they didn’t care — but you just got to play hard the entire game, especially to do what we want to do.”

Arizona’s other senior starter, Mark Lyons, had 14 points but shot 1-of-9 from the field.

Sophomore guard Nick Johnson had four points and three turnovers in 23 minutes.

It’s not Johnson and Lyons’ fault, but the play of the backcourt — in particular the point guard — sets the tone for the rest of the team.

“The solution isn’t one,” Miller said. “The solution is the whole.”

— Zack Rosenblatt is a journalism senior. He can be reached at sports@wildcat.arizona.edu or on Twitter via @ZackBlatt.