And while it's difficult to get anyone in the NFL to admit they are surprised by anything, Harris has been a surprise -- at first a pleasant surprise and then a needed surprise.
Or as Denver defensive coordinator Joe Woods has put it: "We always tell the story that he was basically one day away from being cut just off of practice in [the 2017] offseason. He just turned it on. [Defensive line coach] Bill Kollar has done a great job with him. He is one of our most productive players. He's just very smart, plays with great leverage and is just a natural playmaker back there."
Broncos coach Vance Joseph also has offered this on Harris: "My first spring here when I watched Shelby work out, I told Kollar, 'He's got about a week before we cut him.' He was that bad that spring."
Harris is no stranger to being cut. He has been waived five times in his career by three different teams -- the Oakland Raiders, New York Jets and Dallas Cowboys -- since joining the league as a seventh-round pick by the Raiders in 2014.
Twenty months after that first wobbly spring with the Broncos, Harris is now a regular in the defensive line rotation as a versatile athlete who can, and has, played as a defensive end and a nose tackle. Harris has played in more than a third of the defense's snaps this season and is one of six Broncos with at least one sack and an interception.
"I guess the light came on," Joseph said. "... The guy's been playing really good football since I've been here. He's just a real guy. He rushes the passer, he's stout when he needs to be, can play multiple spots, just a good football player."
Harris offered his own assessment.
"You just keep working," Harris said. "In those times where you get cut, you look at it and see what the circumstances were and what you need to do. But sometimes, it's just taking advantage of opportunities you have. You keep working for those opportunities and when you get them and look at yourself too. But if you stop working, nobody is going to give you another chance. I kept working."
Harris' best moment in a sometimes troubled year for the Broncos sealed one of the team's best wins. It was Harris who snatched Ben Roethlisberger's pass in the closing seconds of a 24-17 victory over the Pittsburgh Steelers in Week 12.
The interception came on a third-and-2 from the Broncos' 2-yard line with 1 minute, 7 seconds to play. It also came on the same day Harris' wife gave birth to a daughter. Harris called it "living my best life."
He is one on a long list of impending free agents for the Broncos, as Harris is scheduled to be a restricted free agent in March.
"I feel like I still have a lot of potential and that I'm still improving," said Harris, who gets a chance to face the team that drafted him on Monday night in Oakland. " ... I know this business and I approach it like every day I have to go out, practice or games, and show everything I can do. I won't change that; I want to finish out this season strong. I think I've shown some of my game, but I think I can be better. I do."