MLB.TV Help Center
How do I view MLB.TV games in full screen?
To view a game in full screen in the MLB.TV Media Player, click on the arrow icons in the bottom right corner of the Media Player. Once in full screen, to go back to the default player size either hover over the toolbar and click again on the arrow icons, or press the ESC key on your keyboard.
If you do not see the square icon on the bottom of your media player, the zoom functionality of your browser may be zoomed in too much to see the entire media player. To resolve this, go to your browser's "View" menu and select either "100%" or "Actual Size" to restore the browser to the default view.