The Chargers were measured and strategic in free agency and the NFL draft, focusing heavily on the offensive and defensive lines while making subtler additions at wide receiver and in the secondary.

In fact, one of their biggest offseason additions was in the coaching ranks rather than personnel. The addition of new offensive coordinator Mike McDaniel could provide as big a payoff as any player they added to the roster.

McDaniel’s arrival will go a long way toward sorting out some of the key positional decisions the club faces this offseason and in training camp.

Here are the three biggest battles to keep an eye on:

Guard

The Chargers are making wholesale changes to their interior offensive line, and both guard spots are up for grabs. Cole Strange was signed in free agency. While he has the inside track on one of those jobs, he should by no means be considered a sure thing based on his underwhelming four-year body of work.

Jake Slaughter, the club’s second-round pick out of Florida, projects as the long-range center. But with Tyler Biadasz signed in free agency, Slaughter will begin his NFL career at guard. The skill set is clearly there, but it would be presumptuous to believe he will make a seamless transition. If he’s slow to master the change, it could open the door for Trevor Penning and Kayode Awosika to earn a starting job.

The Chargers doubled down at guard in the draft, selecting Boston College’s Logan Taylor and Oregon’s Alex Harkey in the sixth round. Both will get every opportunity to compete for playing time.

For all of the candidates, proving they can excel in McDaniel’s offense will play a big part in the decision. And that process is already well underway.

WR3

On paper, this doesn’t seem like much of a battle with Ladd McConkey, Quentin Johnston and Tre’ Harris all returning. But the Chargers drafted Mississippi State speedster Brenen Thompson in the fourth round, and he feels like a perfect match for the scheme under McDaniel.

The easy comparison for Thompson is Tyreek Hill, a fellow 4.2-second 40 guy with a similar build to the 5-foot-9 Thompson, who posted an SEC-best 1,054 receiving yards last year. If he can be anything close to Hill, he will push for playing time sooner rather than later.

That said, Harris was solid in his rookie season last year with 30 catches for 324 yards, and the needle is pointing up on the former Ole Miss standout. He and Thompson could be headed for a key battle through the remainder of the offseason and training camp.

Also, keep in mind: Keenan Allen, the Chargers’ leading receiver last year, remains a possibility to return. The next month will tell the club a lot about whether they need to put a full-court press on Allen to convince him to come back for another year.

Safety

With the Chargers playing significantly with three safeties, and Derwin James’ ability to play all over the field, filling the traditional strong and free safety positions will be a big focus during OTAs and training camp.

That puts a spotlight on veterans Tony Jefferson and Elijah Molden and second-year prospect RJ Mickens.

Jefferson and Molden are penciled in as the starters at those spots, with James primarily playing out of the slot. But Mickens and rookie Genesis Smith could have something to say about that.

Jefferson is coming off a career-high four interceptions, and his 57 tackles were his most in seven seasons. Molden had 58 tackles in 12 games, and Mickens was solid as a rookie with 29 tackles and two interceptions in 12 games, including six starts. All three have an opportunity to hold onto their roles and, in Mickens’ case, potentially build on his.

But don’t sleep on Smith, the Chargers’ fourth-round pick out of Arizona, pushing Jefferson for a starting job. He needs some work on his tackling, although the Chargers believe it’s just a matter of him using better technique. Aside from that, he has the necessary skill and mindset to patrol the back end of the Chargers’ defense. He has a big opportunity ahead of him through the offseason and training camp.