The San Francisco 49ers are making changes to their defense in 2017, switching from a 3-4 to a 4-3 hybrid we see in Seattle to a certain extent. They will still spend a lot of their time in the nickel, but this could result in some shifting around of responsibilities.
The 49ers lacked many strengths last season, but the defensive line offered some positives in an otherwise dismal year. The team lost Ian Williams before the season even got going, but they got strong work from rookie DeForest Buckner. Losing Williams was a disappointment, but losing Arik Armstead was an even bigger disappointment.