This game is great for 2 players but can be adapted for more. It requires a little more thinking than other games as strategy plays a part in it.
A shot at Bull determines who starts.
The sections on the board that are in use in this game are 10-20 and Bull. A player can throw darts at any of these. If player 1 hits the number 20 three times, they have activated the 20's for themselves (trebles and doubles count). Anytime that player 1 hits the 20's after the initial 3 times, they score the number of points they hit. For example, if player 1 hits three 20's on their 1st go, they would activate it. If on their second go, they hit the 20 twice, they would actually score 40 points. I hope this makes sense!
Player 1 can keep scoring on the 20's until player 2 hits the 20's three times. Once the second player has hit the 20's three times, the number 20 is closed, or “bowled out” if you prefer, and neither player can score on it. This then applies to all the other numbers from 10-19 and bull. You can go in any order - there is nothing saying you have to start with 20.
The game ends when all the numbers have been bowled out and there is nothing left for either player to score with. The game could feasibly go on forever because player 1 could activate the 20's and keep scoring and scoring on them, whilst player 2 activates the 19's and keeps scoring and scoring on them. This rarely happens as it is usual for the person who initially takes the lead to defend it by trying to stop their opponent from scoring.
Difference with Bull - Aiming for Bull is effectively the same thing, but hitting Outer Bull gives you one point, and hitting Inner Bull gives you two. Once Bull is activated, you score 25 and 50 points for hitting Outer Bull and Inner Bull respectively. It is “bowled out” in the same way as other numbers.
Best way to keep score is to use a tally and cross out the whole line once both player have hit a number 3 times. Having a cumulative score helps too.