Leading UK player Jon Barnes talks about how to make sure all your rolls are legal, specifically discussing section 4.1 of the UKBGF Rules…
In matches played without a baffle box a valid roll consists of the dice being shaken vigorously in a cup and then rolled out of the cup onto the playing surface of the board. During this process the dice should not touch the player’s hand and the cup should not touch the board. The dice must roll freely and come to rest lying flat on the playing surface of the board to the roller’s right of the bar. If this is not the case, the roll is deemed invalid and must be retaken.
https://youtu.be/Plg2P_MULng