Although players have been inside EverBank Field for several weeks training for the upcoming season, Jaguars coach Gus Bradley's fourth year doesn't officially begin until Monday when he is allowed to address the full squad.

The Jaguars' two-month offseason program will include 10 organized team activity workouts in late May/early June and finish with a mandatory mini-camp June 14-16 (everything else is voluntary).

Since the Jaguars were last together Jan. 4, Bradley has signed a one-year extension, Todd Wash has been promoted to defensive coordinator and seven free agents have been added.

"There's a lot of excitement, but the big thing is, we need to go to work," Bradley said in an interview Thursday. "We'll have different things going on - it's the offensive staff's second year teaching the system. Last year, the challenge was learning it; this year, the challenge is to hold each other accountable to a standard.

"Defensively, there will be some subtle differences in what we do - a different approach - so they'll get a feel for that part of it. We're going to really try and grow in a lot of areas the first two weeks and then progress through OTAs."

Here are four Jaguars issues to follow this spring:

CLARITY AT CENTER

The Jaguars are looking at a fourth center in as many years - Brad Meester retired after 2013, Luke Bowanko was put on the bench after 2014 and Stefen Wisniewski wasn't re-signed after 2015. The Jaguars offered Wisniewski one- and two-year contracts (money unknown), but he decided to sign with Philadelphia to compete for a starting guard spot.

Uninterested in bringing Wisniewski back and unwilling to jump into the Alex Mack fray, the Jaguars have been in a holding pattern at a position they call the second-most important on the offensive line after left tackle. The in-house candidates are Bowanko (no snaps last year), right guard Brandon Linder (coming off shoulder surgery) and Tyler Shatley (no NFL center snaps).

Earlier this offseason, general manager Dave Caldwell said it was "trending," toward Linder being moved to center. Now?

"I think Gus and the coaches are working through that now - I don't think they'll have any answers until after the draft on that one," Caldwell said.

Answer A from the draft: The Jaguars draft a center and anticipate him starting Week 1 against Green Bay. Alabama's Ryan Kelly visited the team earlier this month, the only center to do so.

Answer B from the draft: The Jaguars draft a guard and move Linder to center. The Jaguars haven't brought in any guards for a pre-draft visit.

By the time OTAs start May 23, it would make sense to have some center clarity.

TRANSITION TO WASH

Last spring was all about how new offensive coordinator Greg Olson would get his group up to speed. The Jaguars improved from 15.6 points per game to 23.5 and from 289.6 yards to 348.8. Can Wash have the same kind of impact on the defense?

The Jaguars allowed 375 yards and 28 points per game last year. Bradley turfed Bob Babich, but promoted Wash instead of embracing a complete overhaul. And when free agent opened, the Jaguars spent to sign defensive tackle Malik Jackson, safety Tashaun Gipson, cornerback Prince Amukamara and a top-draft-pick-to-be-named. Plus, Dante Fowler will debut and Sen'Derrick Marks will return from injury.

The expectation for this Jaguars defense shouldn't be that it will be greatly improved; it should be that they'll be less awful.

"It will be a re-commitment to the details and a re-commitment to a standard," Bradley said. "Holding them accountable - it's one of Todd's strengths. We've seen that in how he handles the defensive line and now I think it will filter through the entire defense."

BUILDING CHEMISTRY

Already full of newbies (the aforementioned Jackson, Gipson and Amukamara), the Jaguars are expected to add multiple draft picks.

The Jaguars will then begin a race to get ready for an opening-month quarterbacking gauntlet of Aaron Rodgers, Philip Rivers, Joe Flacco and Andrew Luck.

The offseason program will be important to installing the tweaked scheme, but also integrating Fowler, Jackson, Amukamara, Gipson and the draft class to a group that returns Marks, Roy Miller, Jared Odrick, Telvin Smith, Paul Posluszny and Davon House, among others.

"I agree with that, big-time," Bradley said of needing to build chemistry. "We've signed free agents so it's bringing the mix together and playing as a unit. You've heard me say in years past how important communication is and how important discipline and understanding the system is. We have to speed that part up."

Assuming the offense will again be mostly productive, even a slightly-better defense will give the Jaguars a puncher's chance this fall.

NEW ROLES

The Jaguars used the second overall pick in 2013 on left tackle Luke Joeckel, the hope being he would anchor the offensive line for the next decade. He'll enter his fourth training camp as the decided underdog in his competition against newcomer Kelvin Beachum (who will be out until August because of a knee injury).

The Jaguars used the 36th pick last year on tailback T.J. Yeldon, the anticipation being he would kick-start a dormant run game. He'll enter his second training camp seeing his workload decreased because of newcomer Chris Ivory, a 1,000-yard rusher in 2015 for the Jets.

Bradley, naturally, is confident Joeckel and Yeldon will respond positively.

"Great. Unbelievable," Bradley said of his talks with both players. "I've talked to Luke more than I have T.J. … Luke's been outstanding. He's focused on what he needs to do and how needs to improve.

"From everything I've heard, T.J. has had a tremendous off-season so we're excited to get him back here. I don't think Chris will be his focus, it will be about what he needs to do."

Ryan O'Halloran: (904) 359-4401