JACKSONVILLE – Alan Ball has no doubt.

Even considering the results of the last two weeks, and even considering the changes in the defensive lineup this week, the Jaguars' veteran cornerback firmly believes this can be a good defense.

He has seen the evidence, and believes in it.

Yes, the Jaguars rank last in the NFL in yards and points allowed, and the defense has allowed 78 points over the last two games. But Ball said the unit has played well at times this season.

And he believes that can still be the real defense.

"I'm not going to say it's like a switch that can turn on and off, but I look at the quarters we played well in,'' Ball said Thursday as the Jaguars (0-3) prepared to play the San Diego Chargers (2-1) at Qualcomm Stadium in San Diego, California, Sunday at 4:05 p.m.

"If you look at the season it's not like we played bad all season. There are times you say, 'Where is that defense at?' I think that defense is still here. We just have to put it on the forefront and play like that every game."

The key to doing that? Defensive players on Thursday discussed that. And while many observers wonder if the presence of rookie quarterback Blake Bortles and a potentially improved offense could take pressure off a defense that is allowing 466 yards a game, defensive players pointed to themselves.

Jaguars Head Coach Gus Bradley has talked a lot this week about trust – i.e., each defensive player trusting and believing that the player next to him will be in proper position. It's part of Bradley's "Do Your Job" mantra, and players said it's critical to improving this week.

"It's trust in the sense that on the field everybody's going to take care of his assignment and you have to trust the guy next to you," middle linebacker Paul Posluszny said. "You have to realize you don't have to worry about his job and you need to take care of your own. Then, the group as a whole will play really, really well. We've been short in that area."

Safety Johnathan Cyprien said the idea is not to try to make up for someone else's mistakes, but for each player to do his responsibility so well that he ends up at the ball.

"What you want is the whole defense doing their job, and once you do your job it's a race to the ball," Cyprien said.

Posluszny said without question there is a sense of urgency to improve now not later.

"Our guys are very, very locked in," Posluszny said. "Whatever we've been doing up to this point has not been allowing us to prepare and play to the best of our abilities. Whether guys are more focused now, more on the details, studying a little more or practicing a little harder – it's all the little increments and improvements that guys are starting to concentrate on."

The Jaguars this week made two changes to the starting lineup, moving Josh Evans into the starting lineup at free safety over Winston Guy, Jr., and J.T. Thomas into the starting lineup at Otto linebacker over LaRoy Reynolds.

While the moves were not designed to "shake up" the defense, Posluszny said such moves can create an urgency.

"When something like that happens, it makes you very aware that if you don't perform at a high level you can easily be replaced,'' he said.

Ball agreed.

"I think it can," Ball said. "I think it can stress that we're looking for a job to be done a certain way. We're looking for the guys who can do it. It's important. It goes hand-in-hand with what we're trying to accomplish, and guys being accountable.

"It can send a message of, 'Hey, we're looking for guys who can do this and we're going to keep looking for guys who can be the exact fit for the things we want to do.'''

Also around the Jaguars:

*Thomas is getting a big chance on Sunday. But the fourth-year linebacker said that's not the priority. Thomas will start against San Diego, taking over at the Otto linebacker position for Reynolds. "It's a really cool opportunity, but it's really the same thing for us all the time – just being able to contribute and be able to be accountable," Thomas said. "Maybe me being one of the older guys I'm a little more versatile, but I look forward to the opportunity." Thomas, who joined the Jaguars off waivers from Chicago shortly before the 2013 season, has played both inside and outside backer with the Jaguars, and was backing up Posluszny in the middle before the injury. "It makes you a better linebacker overall," Thomas said. "It's been a smooth transition to the Otto mostly because of watching Poz, watching how he's on top of the details." Thomas said his focus this week will be on continuing to play a significant role on special teams while handling starting defensive duties. He has been one of team's top special teams players since his arrival. …

*Posluszny missed practice on Wednesday with an ankle injury sustained against the Colts last week. The area is swollen, but Posluszny played through it against Indianapolis and has little question he will continue to do so. Asked Thursday if he thought the injury might keep him out against San Diego, he looked at the questioner and said, "Come on." …