San Diego/L.A. Chargers – Ryan Leaf
Laughably, many people thought that Ryan Leaf had more upside than Peyton Manning in 1998. The San Diego Chargers drafted him with the second-overall pick and felt smug about it. But this turned into one of the biggest disasters in franchise history. Leaf had three seasons in San Diego but it didn’t work out (via Sportskeeda).

He threw 13 interceptions with just two touchdown passes in his rookie year. Then his sophomore season was a write-off because of injuries. Finally, the Chargers went 1-15 in 2000 before they released him. Leaf also had drug problems and lacked maturity. This hurt the Chargers a lot because Eli Manning later refused to play for them.