Earlier today 2K Sports, on its Facebook page, confirmed March 8 as the release date for MLB 2K11.
While we're pinging Sony to verify MLB 11 The Show comes out the same day, traditionally multiple league-licensed products all come out on the same day. An exception would be NHL 2K11, which was a Wii-only release. It arrived on Aug. 24, two weeks before EA Sports' NHL 11 and Wii-only NHL Slapshot.
This year, both baseball games released on the first Tuesday of March. Next year, Fight Night Champion is out March 1. The two sports have vastly different appeals and divergent fan bases, but it's still quite a sports showdown early in the year.