I haven't flown on BA with WiFi on board but if it's anything like the WiFi on Aer Lingus (and Aer Lingus seems to be a beta testing airline for BA at times) then it probably won't be reliable or fast enough to stream live video (and even with a good land based connection streaming sites can be poor quality).

Or though not ideal you might consider internet radio to listen to the game live, WiFi on board should be good enough for this.