Georgia Tech coach Paul Johnson will blow the whistle Saturday for the first practice of the preseason, starting the countdown to the season opener against Alcorn State on Sept. 3 at Bobby Dodd Stadium.

There is technique to be refined, mettle to be tested, conditioning levels to be augmented. In the heat of the practice fields and in the cool of the meeting rooms, Johnson and his staff will have to sort out their depth chart and develop the plan to pursue the Yellow Jackets’ fourth ACC championship. The following are five subplots in the formation of the 2015 Tech football team.

Jobs on the line

Perhaps the most significant competitions that will take place in preseason camp will be for the starting jobs at wide receiver, A-back and B-back, where the likes of DeAndre Smelter, Charles Perkins and Zach Laskey have moved on after helping drive the Jackets to the Orange Bowl championship.

At wide receiver, Micheal Summers and Ricky Jeune will try to fend off Antonio Messick and others. At the ACC Kickoff, quarterback Justin Thomas said he had worked a lot with Summers and helping him break some bad habits. At B-back, Marcus Allen goes in as the No. 1 after switching back to the position in the spring following injuries to C.J. Leggett and Quaide Weimerskirch. Graduate transfer Patrick Skov will challenge, as will two freshmen.

That said, coach Paul Johnson said he feels comfortable with Allen as his B-back. At A-back, Isiah Willis and Broderick Snoddy (pronounced “100 percent” by Johnson after his broken leg in November) have a host of freshmen pursuing them.

“I think we’ve got good skill guys,” Johnson said. “We’ll see. They have to play, but I think they’re pretty talented.”

Go time for Kallon, Devine

Defensive tackle Francis Kallon and guard Shamire Devine were two of the most intriguing Tech recruits in recent memory. Kallon arrived as a raw, athletic defensive lineman from Central Gwinnett High who grew up in England and only began playing football in spring practice of his junior year. Devine was a plus-sized offensive tackle prospect with agility out of Tri-Cities High.

In two seasons for Kallon and one for Devine, their on-field contributions have not matched the considerable expectations that attended their arrivals, perhaps not surprisingly. However, both could play integral roles in the team’s success this season.

Devine is penciled in as the replacement at right guard for All-American Shaquille Mason. Coaches hope that Kallon can be a productive member of a defensive tackle rotation with Adam Gotsis and Jabari Hunt-Days (if Hunt-Days regains his academic eligibility, as expected).

If Devine can demonstrate improved conditioning and lock down the spot, he will enable the four returning starters to stay in their spots. If Kallon can prove a capable sub, that will free Patrick Gamble to swing to defensive end and add stability to that position.

Hunt-Days, Whitehead resurface

Hunt-Days will have plenty of attention himself. Given the glowing reviews from coaches and teammates last fall and the spring, when Hunt-Days was academically ineligible, the defensive tackle can give the Jackets a huge boost if he is equal to the fanfare. Regrading his eligibility, Johnson said earlier in July that “I think he’ll be fine.”

Almost forgotten is another defensive lineman who also sat out last season, transfer Kenderius Whitehead, who is second on the depth chart at one end spot behind Rod Rook-Chungong. Whitehead, who showed well in the spring game, could end up playing a significant role.

The more playable depth that defensive line coach Mike Pelton can accumulate, the fresher and more capable of making an impact the line can be late in games and in the back half of the season.

Opportunities for freshmen

Perhaps more than in most seasons, Tech’s incoming freshmen have a chance to enter the conversation for playing time. Particularly at the running back and wide receiver spots, there is opportunity for freshmen to play immediately.

At the ACC Kickoff, Johnson mentioned that Thomas had spoken well of freshman wide receivers Brad Stewart and Christian Philpott in their work in seven-on-seven passing drills. At A-back, Nate Cottrell, Omahri Jarrett and TaQuon Marshall can earn A-backs coach Lamar Owens’ attention with effective perimeter blocking. B-backs Mikell Lands-Davis and Marcus Marshall have expressed their goal to play immediately.

Linebacker is another spot where there could be an opening. Accordingly, freshmen Victor Alexander, Tyler Cooksey and Brant Mitchell are among the highly touted members of the class.

Defense needs to improve

Johnson isn’t one to sugarcoat, and so it was that, when Tech’s defensive statistics were brought up at the ACC Kickoff, he cut off the questioner with, “Yeah, we were awful.”

The Jackets improved over the course of the season and had an uncanny knack for forcing turnovers, but finished in the bottom 15 percent nationally in yards per play (6.32), third-down efficiency (45.56 percent) and nearly so in completion percentage (62.9 percent).

However, Tech returns eight starters and should receive a lift from Hunt-Days and Whitehead.

“I think we should be better on defense as a whole,” Johnson said. “I think we will.”

Defensive players have professed a desire to earn recognition alongside the Jackets’ prolific offense.

“Just be a physical, feared defense,” linebacker Tyler Marcordes said.