As the 2021 offseason winds down and training camp approaches, we're turning our attention toward the season. Over the next few days, we'll take a look at each of the position groups on the Broncos' roster before finishing our training camp preview series with a look at some of the top questions facing the team. In our look at each position, we'll fill you in on what we know about the group and what we hope to find out during training camp. We'll also identify a player to keep an eye on when practices and the preseason get underway shortly.We continue the series with a look at the Broncos' defensive line.

What we know:

As the Broncos tinkered with the rest of their roster this offseason, they filled their defensive line needs largely from within. After the team released veteran Jurrell Casey early in the offseason, Denver prioritized re-signing Shelby Harris and retained the veteran defensive end on a three-year deal. The team previously extended nose tackle Mike Purcell during the 2020 season, and the Broncos had Dre'Mont Jones waiting in the wing to assume the final starting spot.

Denver did make a couple of additions, as the Broncos signed Shamar Stephen in the second wave of free agency and added Marquiss Spencer in the seventh round of the 2021 NFL Draft.

The Broncos invested plenty in their defense this offseason, but their level of success will likely start up front. A year ago, the unit was battered by injuries as they lost Casey and Purcell for the season and Jones and Harris for extended periods of time. After ranking seventh in rushing defense over the final 12 games of 2019 after Purcell entered the lineup, Denver struggled at times to contain the run in 2020 after Purcell's season-ending injury in Week 4. The Broncos will look to rebound from their No. 25 ranking in rushing defense from last season and will hope to enjoy better health this year.

What we need to learn:

Who will step in behind the starters?

The Broncos' starting rotation appears set, as Harris, Purcell and Jones should form a solid initial front for Denver's defense. The questions will come later in the rotation. The Broncos have several options, but many of the team's depth pieces are unproven. Spencer will have to adjust quickly to the NFL game, while second-year lineman McTelvin Agim must take a step forward from his 2020 campaign in which he played just 13 percent of the team's defensive snaps. Stephen and Williams seem like the safest bets to push for roster spots, as Stephen has started 65 games in his NFL career and 45 over the last three years. Williams, meanwhile, started 11 games for Denver in 2020 after a four-year hiatus from playing time. Jonathan Harris, Isaiah Mack and Deyon Sizer will also push for roster spots.

For Denver to reach its desired level of defensive success, it's likely the Broncos will need one or two of these reserve players to step in at times and play at a high level. During training camp and the preseason, we should get a good idea about which players will carve out those roles.

Purcell's health will also be worth monitoring during training camp, as he did not practice during the offseason program as he returns from a Lisfranc injury. The Broncos' run defense fell off in 2020 after his injury, and his return to the field is perhaps an understated storyline of this offseason.

Player to watch:

As many focus on how outside linebackers Bradley Chubb and Von Miller will lead the Broncos' pass rush, Jones also merits attention. The 2019 third-round pick recorded 6.5 sacks and 11 quarterback hits in eight starts in 2020, and more than half of those sacks came over the final four weeks of the season.

In 2021, Jones could have a real chance at reaching double-digit sacks. Offenses will likely have to dedicate extra resources to stopping Miller and Chubb, which should free Jones up for one-on-one matchups along the interior of the defensive line. Jones should also benefit from an improved secondary and from scenarios in which quarterbacks have to step up in the pocket to avoid Miller and Chubb. Jones recorded several of those second-effort sacks in 2020, and he should be the beneficiary of more this season.

"I think 10 sacks is very attainable," Jones said in June. "Guys like Chris Jones, Grady Jarrett, Cameron Heyward and Aaron Donald made it cool to be an inside guy and get 10 sacks. It's very attainable and I don't expect anything less from myself. I think that's a goal of mine that I can reach. I'm going to try and reach it."