 Blackball Rules enable an opponent's ball be potted legally at any time during the frame - provided one of your own colours is also potted during the same shot, this is called a skill shot and is illegal in World Rules.After a foul in Blackball Rules, the incoming player has one free shot (they may accept the cue ball in-position as it lies on the table, or take cue ball in-hand, and place it in baulk) where they may legally play any ball.Following the free shot, the player will have one visit remaining regardless of the free shot outcome.