In three seasons with the Jayhawks, Armstrong registered 142 combined tackles, 34.5 for a loss, 15.5 sacks, eight passes defensed, six forced fumbles, and three fumble recoveries. During his sophomore campaign in 2016, he brought down the quarterback 10 times while recording 56 combined tackles with 20 for a loss and was named first-team All-Big 12.
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At the NFL Scouting Combine, the 6-foot-4 and 246-pound Armstrong had a 40-time of 4.87 seconds, a vertical jump of 30 inches, a broad jump of 118 inches, completed the three-cone drill in 7.12 seconds, had 20 reps in the bench press, a 20-yard shuttle time of 4.23 seconds, and a 60-yard shuttle time of 11.82 seconds.
NFL.com projects Armstrong to be a fourth- or fifth-round draft pick.
Lance Zierlein of NFL.com, who compares Armstrong to Kamerion Wimbley, wrote the following within his scouting report:
"Armstrong is an intriguing prospect with the build and fluid athleticism of a shooting guard. Armstrong's drop in production can be attributed to a change in scheme that asked him to play run first and pass second. His game revolves around athletic ability over technique, but his poor forty times at both the Combine and his pro day could cause concerns. Armstrong has the tools and upside to become an eventual starter at outside linebacker in a 3-4."
Measurables
Height: 6-4
Weight: 246 lbs.
NFL Scouting Combine
40-time: 4.87 seconds
Vertical: 30 inches
Broad jump: 118 inches
3-cone drill: 7.12 seconds
Bench press: 20 reps
20-yard shuttle: 4.23 seconds
60-shuttle drill: 11.82 seconds
College Statistics
| Year | G | Tkl | Loss | Sk |
| 2015 | 12 | 23 | 5.0 | 3.5 |
| 2016 | 12 | 56 | 20.0 | 10.0 |
| 2017 | 12 | 63 | 9.5 | 2.0 |
| Totals | 36 | 142 | 34.5 | 15.5 |