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Bud Dupree immediately knew that something was wrong. Dupree, the Pittsburgh Steelers' talented outside linebacker, smacked the ground several times after falling to the turf with less than six minutes remaining in his team's 19-14 win over the Baltimore Ravens to close out a whacky Week 12 that concluded with a Wednesday afternoon game. Less than an hour after the game, reports surfaced that Dupree, whose 19.5 sacks over the past two years is the second-highest total on the team, had suffered a torn ACL, thus ending his sixth (and possibly final) season in Pittsburgh. 

The loss of Dupree is a big one for the 11-0 Steelers. He's been a big reason why Pittsburgh leads the NFL in scoring defense, sacks and turnovers forced. Over the past two years, he has been half of arguably the best outside linebacker duo in the NFL with fellow former first-round pick, T.J. Watt. Dupree, who had been playing under the franchise tag, is the second Steelers' defensive starter to suffer a season-ending injury. Devin Bush, the 10th overall pick in the 2019 draft, tore his ACL five weeks into the season. Pittsburgh replaced Bush with Robert Spillane, a former undrafted rookie who had 11 career regular season tackles prior to the 2020 season. Spillane has remained in the starting lineup despite the Steelers' acquisition of former Jets linebacker Avery Williamson just before the trade deadline. 

While they sought outside help to address the loss of Bush, the Steelers have more depth at outside linebacker to address this issue. Dupree's backup this season has been rookie Alex Highsmith, a third-round pick who recorded 15 sacks and 21.5 tackles for loss during his final season at Charlotte. An immediate special teams contributor, Highsmith has also made the most of his reps with the Steelers' defense. In Week 8, his interception of Lamar Jackson at the start of the second half set up a touchdown, as Pittsburgh rallied from behind to defeat the Ravens in Baltimore. A week later, his first quarter sack forced the Cowboys to settle for a field goal, as the Steelers left Dallas with a 24-19 win. 

Despite making it to the NFL, Highsmith continues to maintain an underdog mentality. 

"Being a [college] walk-on, I had a mentality and a work ethic a lot of people didn't have, so that's one thing I think I bring to the table," he said during the spring, via Stephen J. Nesbitt of The Athletic. "(It) was my story, something I wouldn't have wanted any other way. I've always had this walk-on mentality ever since I got to college. That's just something I'm bringing to the NFL as well."

Highsmith has also taken advantage of playing behind two of the NFL's most productive outside linebackers in Watt and Dupree. 

"They're two of the best at what they do in this business," Highsmith said earlier this season. "It's awesome being able to learn from them. I try to ask them questions as we watch film or during meetings. I watch their film to see what moves they use. I've picked up a lot from their game. I'm going to continue to pick their brains and do whatever I can to reach their level."

While Highsmith will likely replace Dupree in the starting lineup, Ola Adeniyi, a former undrafted rookie out of Toledo, should also receive an elevated role on the defense. After spending most of his rookie season on injured reserve, Adeniyi has developed into a quality player on special teams over the past two years. His first splash play in the NFL took place on special teams, as his forced fumble of Chester Rogers set up a field goal in Pittsburgh's 26-24 win over the Colts in Week 9 of the 2019 season. Tegray Scales, who is currently on Pittsburgh's practice squad, may be summoned to join the team's 53-man roster in the coming days. 

Since 2018, Adeniyi has worn No. 92, a number previously worn in Pittsburgh by James Harrison, a former Defensive Player of the Year who retired as the franchise's career sack leader. On Thursday morning, Harrison posted a video during a visit with Dr. James Bradley, the Steelers' head team orthopedic surgeon. While he hasn't played since having a brief stint with the Patriots at the end of the 2017 season, the 42-year-old Harrison has continued to stay active in retirement. Harrison would provide a veteran presence to a unit whose oldest player is Watt, who played alongside Harrison during his rookie season. The five-time Pro Bowler would likely be asked to play only in pass-rush situations. 

Regardless of who else may join the ranks, it appears that the Steelers have the players to help replace Dupree, who will now turn his attention towards the 2021 season.