The Buffalo Bills will shift to a 3-4 defense under new defensive coordinator Jim Leonhard, a significant change after playing out of a 4-3 base under Sean McDermott for the past nine seasons.

Several players will be affected by this transition, but the move may bring back memories of a similar change in Buffalo a decade ago, much like when a coaching change was also made.

History may not dictate the future, but Bills fans may recall what happened the last time they made a major defensive shift in 2015.

Who changed Bills to 3-4 defense last time?

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After a 9-7 season in which Buffalo narrowly missed breaking one of the longest playoff droughts in North American professional sports, former New York Jets head coach Rex Ryan replaced Doug Marrone in 2015 and brought a new defensive philosophy with him.

The Bills’ 4-3 defense under Jim Schwartz ranked fourth in both yards allowed and points allowed and led the NFL with 54 sacks. Ryan’s arrival didn’t bring about similar results, however.

Ryan attempted to merge elements of Buffalo’s 4-3 with his preferred 3-4 scheme during his first season in Buffalo, but the defense regressed. In 2016, he implemented a full version of his system alongside his brother Rob, with only marginal improvement.

The regression in 2015 was most evident along the defensive line. Jerry Hughes, Marcell Dareus and Mario Williams combined for 22.5 fewer sacks than the previous season, citing frequent drops into coverage instead of rushing the passer.

Buffalo’s defense fell to 15th in points allowed, 19th in yards allowed and second-to-last in sacks with just 21. The Bills finished 8-8 and missed the playoffs for the 16th consecutive season.

Rex Ryan was fired during the following season and McDermott was hired in January 2017. He lasted nine seasons in Buffalo before being dismissed after a sixth straight playoff disappointment.

How will today’s Bills personnel be affected by change?

Leonhard’s 3-4 scheme will primarily impact players who have spent their entire careers in Buffalo, especially along the defensive line.

Greg Rousseau, a former wide receiver in high school and an excellent athlete, could benefit from a stand-up outside linebacker role. Second-year defensive tackle Deone Walker has the build to be a nose tackle if he adapts well.

Several players familiar with Leonhard’s system are set to hit free agency in March. If any join Buffalo, their experience will be valuable to veterans like Matt Milano and Terrel Bernard, who are expected to start together as the two inside linebackers. Ed Oliver, a projected 3-technique, could also benefit from the transition

Bills fans will hope the results differ from Ryan’s change. Leonhard faces a tall task to ensure history does not repeat itself.