His 2016 season wasn't as successful, although the entire Bills defense took a pronounced dip and finished just 27th in Football Outsiders' DVOA (defense-adjusted value over average).
General manager Doug Whaley and head coach Rex Ryan were fired, and a new regime led by general manager Brandon Beane and head coach Sean McDermott arrived.
The new brass jettisoned numerous players in an effort to rebuild a franchise that hadn't made the playoffs since 2000. Darby was one of them, and the Philadelphia Eagles picked him up for wide receiver Jordan Matthews and a third-round pick.
Darby's Eagles career has been marred by injuries, but he's been productive when he's been on the field.
A dislocated ankle suffered in Week 1 of the 2017 season kept him out of regular-season action for half the campaign, but he returned and helped Philadelphia win its first Super Bowl in franchise history. In eight games, Darby had 34 tackles, nine pass deflections and three interceptions. He also had 16 tackles and six pass deflections in the playoffs.
His fourth NFL season started with promise thanks to 43 tackles, 12 pass deflections and a pick in nine games, but a torn ACL suffered in Week 10 ended his season.
The 5'11" Darby has proved his worth and turned 25 years old in January. Also, Gregg Rosenthal of NFL.com ranked him as the 13th-best free agent in the class of 2019 and its top cornerback.
If Darby can stay healthy and return to his old form off the ACL injury, Philadelphia is getting a steal.