To watch the video in full screen mode, you will need to rotate your device to view in landscape.
If your video does not change from portrait mode, you will need to check/adjust the settings on your device.
For further information, please view the attached pictures which show a useful step-by-step guide.
STEP 1 PORTRAIT MODE and PLAY-BY-PLAY
STEP 2 LANDSCAPE MODE after rotating the device
STEP 3 Landscape mode and PLAY by PLAY