The data is coming directly from mlb.com, who provides a json feed for non-commercial use. I hope this continues to qualify, since I'm not running ads. :)
http://developer.fanfeedr.com/
2400 API pulls a day for free and I think it includes all the major sports.
Link to the source: http://code.google.com/p/boxscore-junkie/
One suggestion: After the initial team search, it would be nice to be able to browse the teams or games somehow. I liked the surprise of the score and description, and it would be cool to easily browse or view a random game or something like that.