MLB Slugfest is a series of baseball games developed by Sports Mogul, Gratuitous Games and Midway Games, and released by Midway Games for major console systems such as PlayStation 2, Nintendo GameCube, and Xbox. The game bills itself as a more "street" style baseball game, including more mature / aggressive themes, the ability to attack other players, and urban-styled in-game commentary.
As of 2009, there are four versions of MLB Slugfest: 2003, 2004, Loaded, and 2006. Loaded includes the unlockable characters Sub-Zero and Scorpion, as well as other non-traditional players. Loaded was the first (and only) baseball game to receive a T for "Teen" rating by the ESRB. MLB Slugfest 2006 was released on May 31, 2006.
Source: Wikipedia, "MLB Slugfest," available under the CC-BY-SA License.