It could be any hour when University of Hawaii defensive coordinator Kevin Clune’s cell phone will sound — ping! — alerting to another text from outside linebacker Jeremy Castro.

"He has studied (this defensive system) more than any single person," Clune said. "He’ll text me at 2 a.m., ‘Hey, Coach, what do I do on this play?’ ‘Hey, Coach, what should I be doing here?’ He’s always thinking about football."

Castro has had a lot of time to ponder. His last game was in December 2011, when he was a 4-star defensive end as a Vista Murrieta High senior.

He signed with UCLA in February 2012, but was ineligible to enroll that fall because he had not met all of the admission requirements. He then earned a qualifying ACT score, enrolled at UCLA in January 2013, and participated in the Bruins’ spring training before deciding to transfer.

Castro redshirted at UH last fall in accordance with NCAA transfer rules.

Castro and Beau Yap, who played defensive end his first three UH seasons, are the Rainbow Warriors’ No. 1 outside linebackers this spring. Under Clune, who was hired in January, the Warriors have switched from a 4-3 front to a 3-4 base.

"I’m trying to study everything," said Castro, who plays on the left side.

In the new scheme, Castro and Yap can align near the line of scrimmage or in pass coverage.

"It feels good to be out on the field," Castro said. "I haven’t played in a real game in a long time. I’m trying to be a player for Hawaii."

Castro tries to glean information from players such as TJ Taimatuia, a senior linebacker.

"I look up to other guys, but I still have to set an example for myself," Castro said.

During the seven-week conditioning program, 6-foot-3 Castro lost 15 pounds and now weighs 235. His body fat is at 12 percent.

Castro said he hopes to gain 10 pounds in the summer conditioning program that leads to training camp in August.

"I’m trying to put in the work," Castro said. "You have to learn to do things when nobody’s watching."

And if there are questions?

"I’ll text Coach (Clune)," Castro said.

It was in the middle of the conditioning program when Yap was told to move from the defensive line’s group to the linebackers’ area.

"I didn’t think anything about it at first," Yap said. "But, slowly, I realized I was a linebacker."

During Tuesday’s first practice of spring, Yap recalled, "I felt like I was on an island. There was so much space around me."

His run-defending duties entail techniques similar to when he was an end. "I have to work on the passing part," Yap said. "I’m not good at it yet. It’s something I have to learn. I’m going to lean on everyone who has experience at it."

But Clune said Yap has played well in pass coverage. Yap nearly intercepted a pass in team drills on Tuesday, and he successfully soared for a deflection on Thursday.

"First, he has good intelligence to play this game," Clune said of Yap. "Second, he’s quick. And third, he’s an experienced cat out there. I’m pleased to have guys like him. He’s a quiet leader, but he’s a leader."

Even before the move, Yap had hoped to shed weight. He lost 7 pounds and now weighs 255.

"I feel better at this weight," Yap said. "I have more stamina."

In this scheme, Yap will defend tight ends, fullbacks curling out of the backfield or receivers crossing the middle. There will be few plays when he will have single coverage on a receiver.

"There’s a lot more room to move around," Yap said, "and a lot more time to react."