The XBox is addictive and, as such, is antithetical to motivation. I think that it, rather than baseball, per se, is the source of his indifference. Even casual XBox playing has been found to alter the young male brain. See Leonard Sax's excellent book Boys Adrift: The Five Factors Driving the Epidemic of Unmotivated Boys and Underachieving Young Men; here's his website: http://www.leonardsax.com)
I see the harm of extensive video gaming every day in my job as an English professor: first, young women out number young men on my campus (and on college campuses nationwide); and, second, the few young men who are in my classes struggle to conjure up the motivation to come to class, much less the motivation to complete assignments. I hear similar stories from my colleagues who teach in more selective schools.
When my almost 50-year old husband was in elementary school and addicted to 1970s after-school television, he came home from school one day only to discover that the TV no longer worked (his mom removed the tube). As the adult, you control this situation.
Finally, lest I come off as a total fascist mom, my son's words and his accomplishments back me up: one day, when he was a HS freshman (and the only freshman who made the varsity baseball team), he said to me, "Thanks for never giving in to my begging and getting me an XBox." He said this because he saw that he made varsity precisely through hard work, which we facilitated by not caving in to his demands for an XBox.*
*Okay, I'll confess that he did have a Wii, which he won through Boy Scout popcorn sales; however, we would not allow him to play Wii during the week.