sentences:  Because only one of the colours can be "on" at any given time, it is a foul to first hit multiple colours at the same time, or pot more than one colour (unless a free ball has been awarded; see below).If a player fails to pot a ball "on", whether a red or a nominated colour, the other player will come to the table, with the reds always being the balls "on" as long as there are still reds on the table.The alternation between red balls and colours ends when all reds have been potted and an attempt (successful or not) to pot a colour is made after the last red is potted, or when the last red is potted or knocked off the table as the result of a foul and is not replaced.