The Steelers feel good about the pieces they've added to their defense in the offseason. But they won't know for sure that they've upgraded at any of those spots until they start playing regular season games.

That will happen Sunday when they open the 2023 season at Acrisure Stadium against the San Francisco 49ers. And opening against the 49ers is just about as stiff a test for a defense as can be had in the NFL.

In running back Christian McCaffery, tight end George Kittle and wide receivers Deebo Samuel and Brandon Aiyuk, the 49ers have perhaps the best group of skill position weapons in the NFL.

They will present a stiff challenge to a defense that has completely revamped itself in the middle of the field, adding inside linebackers Cole Holcomb, Elandon Roberts and Kwon Alexander, as well as safety Keanu Neal and nickel cornerbacks Chandon Sullivan and Desmond King. King was acquired by the Steelers just last week.

"I think it's just starts with Christian McCaffrey," said Steelers head coach Mike Tomlin. "We have got to respect the dynamic playmaking ability that he has both in the running game and in the passing game.

"He's dynamic in the run game. He's dynamic in the passing game, we better be really careful about being matched up against him in space. He's a one-on-one space winner. They have a lot of one-on-one space winners. He might be the most dynamic one-on-one space winner at running back in the NFL. Kittle might be that at tight end. Debo Samuels might be that at receiver. Their run-after (the catch) ability with their offense of eligibles is really impressive."

It will be a good test for the Steelers, particularly perhaps at inside linebacker.

Holcomb, Roberts and Alexander were brought in this season after the Steelers either moved on from Myles Jack and allowed Devin Bush and Robert Spillane to leave in free agency.

That group produced little splash in 2022, accounting for just one sack, no interceptions and no forced fumbles and nine combined tackles for a loss.

The new group at inside linebacker had a strong preseason presence, but it was just that, the preseason.

The real tests await.

"I think that'll be revealed to play," Tomlin said of whether that group has been upgraded. "I don't live in a hypothetical world. That tape is going to be our walking and talking and breathing resume for the individuals within the collective or from smaller collectives."

No player will test that group quite like McCaffery.

A 1,000-yard rusher and receiver in 2019 with the Carolina Panthers, McCaffery was acquired via a trade by the 49ers midway through last season.

In 11 games with the 49ers, McCaffery rushed for 746 yards and caught 52 passes for 464 yards, scoring 10 combined touchdowns.

The 49ers were 3-3 before acquiring McCaffery and went 10-1 in the regular season after the trade, seeing their points per game average jump from 20.3 to 29.8.

He helps the 49ers be especially dangerous when it comes to the use of play-action, as well as presenting a major challenge when he splits out wide. And that plays right into the hands of head coach Kyle Shanahan's offensive scheme.

Shanahan is considered one of the best offensive schemers in the NFL and will attempt to create mismatches in the passing game.

"It's a coach's challenge from a fundamental and technical standpoint and players' challenge from a tackling standpoint," Tomlin said. "They have got a really solid motor operation offensively of diverse attack. They have got an awesome running game. They have got a supporting misdirection and play-action passing game. They're thoughtfully aggressive in terms of how they go down the field and they do it in a variety of ways. They play really good situational football offensively and allows them to take care of the ball and minimize negativity. They stay on schedule very well,

"But I think that's reflective of Kyle Shanahan and, and he's been around a lot and we've been exposed to him a lot over the years. And I just think that regardless of new and current chess pieces that's kind of reflective of how he has always played over the years, and I have got a lot of respect for what he does and the manner in which he does it. Familiarity doesn't necessarily provide comfort. It just provides focus, as we prepare and work to demand the things that he and they do."

Level of comfort: One of the more interesting battles through training camp and the preseason was the one at left tackle, where third-year veteran Dan Moore Jr. and rookie No. 1 pick Broderick Jones both had impressive showings in the preseason.

Only one can come away the starter, and that was Moore, who started 33 games over the last two seasons at left tackle.

Coach Mike Tomlin said he likes what the team has at that position, with two capable left tackles ready to go, and that Moore earned the starting role.

"I thought he played really well," said Tomlin of Moore. "I thought he showed the growth and maturation that comes with the 1,000 or so snaps that he's played over the last two years. Really comfortable there."

His level of comfort with Moore isn't a bad reflection on Jones, though. It's just that the Steelers have depth, something that any team would welcome, at the left tackle spot.

"Also really excited about what Broderick showed us," said Tomlin. "We were very thoughtful about making sure he got a lot of reps during the course of development, particularly in preseason stadiums. I like the work he did there.

"I feel really good about our left tackle position. I feel really good about Dan's growth and development. I feel really good about the acquisition of Broderick and how bright his future is. I know oftentimes depth charts produce stories, what's wrong with Broderick, etc. There is nothing wrong with Broderick. There was nothing wrong with Cam Heyward when he watched.

"If you have a good team. If you have people playing well, oftentimes it means young, capable guys have an opportunity to watch as they grow and develop. That is the story of the left tackle position and I feel really comfortable about where we are."

Another position where a wait and watch approach is going to be taken right off the bat is at cornerback, where rookie No. 2 pick Joey Porter Jr. is a backup at his spot, particularly after dealing with injuries in the preseason.

"We were able to get him a lot of reps, particularly over the last several weeks," said Tomlin. "Obviously, he missed a game and there's consequences for that from a development standpoint, but he made a lot of plays in team development in Latrobe. Highly competitive. Feel really good about his growth and development and the trajectory of it and what he's able to provide us not only in the short term, but the long term."

Born leaders: The Steelers announced their captains for the 2023 season on Monday, and Coach Mike Tomlin is well aware it's a group that will be depended on for their leadership on and off the field this year.

"The leadership displayed…it can be reflected by our captain voting," said Tomlin. "I am proud of the group this group selected."

The captains are Kenny Pickett on offense, Cameron Heyward and T.J. Watt on defense and Miles Killebrew on special teams.

Pickett is a captain for the first time, a player who showed leadership from the moment he stepped on the field his rookie season and it's only improved.

"I think him being the lone captain on offense is no disrespect to the leadership of others, but probably more of a reflection of everyone's feel of his growth and development, not only as a player, but as a leader within this collective," said Tomlin. "It's reflective of the teams' view of him and his growth and development."

Heyward and Watt are no strangers to the captain role. Heyward is a captain for ninth consecutive year, while Watt is a captain for the third time.

"Cam Heyward and T.J. Watt are guys that have been mainstays here for some time now," said Tomlin. "Not only lead by what it is they do, but the manner in which they do it. The things they do inside stadiums and the things they do outside of stadiums on a day-to-day basis provide a blueprint for others to follow."

This is the second straight year Killebrew was selected as the special teams captain and his leadership will be crucial with some of the turnover that unit has seen.

"I can't say enough about Miles Killebrew and what he has done in that phase since he has been here," said Tomlin. "His kick blocking ability. His passion. His attention to detail. His leadership.

"We are going through a transition in that phase of our team. Arthur Maulet, Robert Spillane, Derek Watt, Marcus Allen who filled up our tackle sheet on special teams a year ago are no longer here. He is probably the most central returning figure. As other guys gain traction, his leadership and production and play making is going to be important to us in that growth and development of that collective and the speed in which it happens is going to be important to us as we embark on this thing."