"The key is that MLB has dumped Microsoft's Silverlight
for its real-time video in place of Adobe Flash. While you can view
Silverlight video in Linux via Moonlight and Moonshine, it's a lot
easier to just use Flash on Linux.
"So, the first thing you should do is install Flash on your
desktop. If you elect to go with Adobe's own, but proprietary Flash
player, you can either download and install it from the Adobe site
or get a copy of the open-source Gnash Flash player. Both programs
are also almost certainly available from your Linux distribution's
software repositories."