Dockery plays Spagnuolo's style of physical, man coverage well. He's been mostly a nickel corner with the Giants, including the two years Spags spent there as defensive coordinator. This could be a good add for the Rams, upgrading their nickel spot between a healthy Bradley Fletcher and Ron Bartell, and making a decent replacement should one of those guys have to miss some time.
This continues the Rams theme of upgrading their depth via free agency, a smart course, if rather unsexy.
Dockery was not offered a RFA tender by the Giants.