No list of this sort for Arizona would be valid without including Kevin Sumlin's horrific tenure. Let's address the elephant in the room: this may seem like recency bias. However, he was handed the keys to a promising team and had one of the most dynamic dual-threat quarterbacks in the country on the roster in Khalil Tate Jr.
Sumlin's background as a standout recruiter for Texas A&M led Arizona fans to thinking they had the guy. With already established California recruiting ties at Arizona, cracking into the Texas recruiting pool was vital to build off of the 2017 season and Foster Farms Bowl appearance, where they fell one drive short of a win.
Sumlin (and his offensive coordinator, Noel Mazzone) proceeded to waste Tate's talents. Arizona finished 5-7 in 2018, with a heartbreaking one-point loss in the Territorial Cup knocking the Wildcats out of bowl contention. 2019 was even worse, as Sumlin attempted some strange sort of dual-platoon approach with Tate and freshman quarterback Grant Gunnell. This was also the beginning of The Streak. The Wildcats dropped a road matchup against Hawaii to start the season. They then ripped off four straight wins, including a last-second win on a missed field goal by UCLA and a 35-30 road win against Colorado on Oct. 5, 2019.
Arizona didn't win another game for two years after that, and Sumlin didn't get to see it happen.
The Wildcats went winless in the shortened six-game 2020 season, and Sumlin punctuated his Arizona career with the infamous "70-7" game against ASU. Arizona fired Sumlin the next day, leaving a mess of a once-promising roster for Jedd Fisch to clean up. Clean it up he did, but not until after having to endure a brutal 1-11 season with the house that Sumlin built.
Though the worst of it all didn't actually happen under Sumlin's watch, he laid the foundations for the worst stretch of football in Arizona history, and he's the worst head coach the program has ever had.