Willis is now in the NFL but four of the conference's top seven sack leaders return in 2017, including Armstrong and a rising sophomore who spent one season under the tutelage of Willis.
Can Armstrong fend off Willis' protégé and a few other disruptive pass rushers to claim the sack title in 2017? Here are five players, ranked, that could lead the Big 12 in sacks this year.
5. Malik Jefferson – LB, Texas
One of two Big 12 outside linebackers with 10-sack potential, Malik Jefferson could earn a top-10 selection in the 2018 NFL Draft with a monster season.
A former five-star recruit from Mesquite, Jefferson is a 6-foot-3, 238-pound menace who will play almost exclusively at weak-side linebacker this year. He has 16 tackles for loss and nine sacks in two seasons.
"He likes it, I know that," head coach Tom Herman said of Jefferson's move outside. "He is adjusting daily to the expectations of him playing with lower pad level, playing more aggressive, playing more physical – and he wants to."
4. K.J. Smith – DE, Baylor
New Baylor defensive coordinator Phil Snow called linebacker Taylor Young their best defensive player "by far" — but there's another stud on the unit, defensive end K.J. Smith.
Smith, a 6-foot-2, 260-pound senior who burst onto the scene with five sacks as a freshman in 2014, didn't record a single sack in 2015 but rebounded with seven last year. He had three sacks in three games in early November and one in their bowl win over Boise State.
3. Reggie Walker – DE, Kansas State
It didn't take long for Big 12 offensive line coaches to know Reggie Walker would be a problem at Kansas State for the next few years. The redshirt freshman recorded five tackles and one tackle for loss in their season opener vs. Stanford and didn't slow down.
He earned Freshman All-American honors — the Wildcats' first defensive player to earn the honor since 2010 — after registering 4.5 sacks, and will become their primary pass rusher with Jordan Willis gone.
2. Ogbonnia Okoronkwo – LB, Oklahoma
Oklahoma fans finally got to see what Ogbonnia Okoronkwo can do when he's healthy.
After two injury-plagued seasons that included three total sacks in nine games, the Sooners' linebacker erupted in 2016, finishing third in the Big 12 with nine sacks.
"I got a lot of other unfinished business here with my teammates,” he said when announcing his return to Oklahoma for his senior season. “I can't leave them behind. I got a lot of high expectations for myself, and I feel like I didn't meet those this year…"
1. Dorance Armstrong Jr. – DE, Kansas
Kansas fans have been waiting a long time for an impact pass rusher. Now they have one of the nation's best in Dorance Armstrong Jr.
The Jayhawks' junior defensive end had a breakout 2016 season and will play on the program's best defensive line in years. He should have plenty of one-on-one opportunities to cause more disruption in 2017 after registering 20 tackles for loss and 10 sacks last year.
“He knows he needs to be the best defensive end in all of college football,” defensive coordinator Clin Bowen said in April. “Not just the University of Kansas. Not just the Big 12. He understands that there are guys at other major universities he is competing with to get to where he wants to get to in his life. And he has embraced that and worked extremely hard on developing his body and his game. He truly is one of those special guys who doesn’t come around very often."