I have two important suggestions for BTSport (hopefully a Mod will look in and pass on the feedback!)
When the online player is in 'full screen' mode, it should NOT go back to normal when you click on another screen.
Create a 'pop-out' player option.
Regarding point 1, Youtube, iPlayer and Sky Player are able to achieve this, so why can BT not? (Sky also use Silverlight....just like BT). I have two monitors, and if I have the football full-screen on one monitor, it renders the second monitor pointless as I cannot click on anything without it minimizing the BT Sport Player on the first monitor.
Regarding point 2, a pop-out player would allow those with only one monitor to view easier as they could move it wherever they like on the screen (again, Sky offer this and use Silverlight, so it must be possible).