Aside from improving a pass rush that last season was the worst in the ACC, the biggest question mark facing Georgia Tech’s defense this season is its secondary.

Gone are the four starters at strong safety, free safety and both cornerbacks from last year’s team that went 3-9.

Chris Milton, Jamal Golden, Demond Smith and D.J. White as a group started 10 of the 12 games and combined for 131 starts in their career. All four are in NFL camps. That was a lot of experience walking out of the north end of Bobby Dodd Stadium.

In as likely starters are A.J. Gray at free safety — whom caoch Paul Johnson said could become one of the school’s all-time great — Corey Griffin at strong safety and Step Durham and Lance Austin at the cornerbacks. Put them together and they have two starts in their career. Lawrence Austin, who will likely play nickelback when Tech switches to a 4-2-5, has 10 starts in his career. That’s not a lot of experience walking into the north end of Bobby Dodd Stadium.

“There are days they do really well and days they struggle,” coach Paul Johnson said. “It’s an ongoing process. You won’t know for sure until they play a few games.”

That level wasn’t bad last season, but it was also a bit of a mirage.

The pass defense was solid in giving up an average of 202.9 yards per game, with 12 touchdowns and nine interceptions. It wasn’t helped by a pass rush that generated just 14 sacks, fewest in the ACC and among the lowest in FBS.

But teams didn’t need to pass much because the run defense was below average, giving up averages of 165.1 yards per game on 4.7 yards per carry. The Jackets allowed 24 rushing touchdowns. All averages were among the bottom five of the ACC’s 12 teams.

Because they were breaking in four new starters in the secondary, defensive coordinator Ted Roof said he had to approach the spring differently in what was being taught. Roof said it was important that the players feel confident because a mistake at those positions can lead to a touchdown.

He said they have been able to install everything he has wanted and is satisfied with how the players are picking it up.

Durham said the players participated in informal seven-on-seven drills against players from Georgia State, Kennesaw State and Clark Atlanta to improve their ability to recognize route combinations and refine techniques and coverages so that they could start camp well. They are also helped by their familiarity with each other. The Austins and Durham are juniors. Griffin is a redshirt junior. They have been around each other for a while.

“It’s good to work with your class members,” Durham said. “We came from the bottom to the top. Now it’s our turn.”

Those turns will come fast. The secondary will face a slew of good quarterbacks, starting in the opener with Boston College’s Patrick Towles, who threw for more than 5,000 yards at Kentucky before transferring. The defense will also face Clemson’s Deshaun Watson, who threw for more than 4,100 yards last year, Miami’s Brad Kaaya, who averaged 277.1 passing yards per game last season, Pittsburgh’s Nathan Peterman, who threw for more 2,200 yards last year, and Duke’s Thomas Sirk, who is as good a runner as passer.

“Hopefully we are going to be up to the level we want to play at,” Johnson said.