Richard Sherman was a great cornerback for the Seahawks. He was also a bit of a cancer in the locker room during his last season with the team. This offseason, after Seattle released Sherman, the cornerback spoke poorly about the organization and specific players, like quarterback Russell Wilson.
There have also been national articles, like the one ESPN The Magazine produced in 2017 citing unnamed players talking about how bad the atmosphere was in Seattle. It is pretty safe to assume Sherman was at least one of the unnamed players talking smack about the Seahawks.