Play begins when the bowler rolls a ball down the lane. There are ten frames in a game of bowling and the bowler is allowed to roll two balls in first nine frames unless he rolls a strike with the first ball. A strike occurs when the bowler knocks down all ten pins with one ball. A strike is entered on the scorecard as an X in the right-hand corner of the frame in which it was bowled.
If the player does not knock down all ten pens with the first ball in the frame, he is allowed to try to know the remaining pins down with his second ball. If he is successful, this is called a spare and it is entered on the scoreboard with a slash mark (/) in the upper right hand corner of the frame in which the spare was earned. The running score in a frame in which a spare occurs is left blank until the player bowls the first ball in the next frame. The number of pins knocked down is added to the 10 points that was earned by the spare.
The player may not pass any part of his body over the foul line when he rolls the ball toward the pins. This line cannot be crossed during the act of rolling the ball, nor may it be crossed at any time afterward. Any pins that are knocked down after a foul is committed do not count and must be replaced so that the frame can be played again with the second ball. A player can therefore roll a strike after committing a foul, but cannot attempt to pick up the spare if he only knocks down some of the pins. If the foul occurs on the second ball, only the pins knocked down by the first ball count.
The number of pins that are knocked down in each frame are recorded and except when a strike or bowled or a spare is picked up. When a strike is bowled the score for that frame is 10 points, plus the number of pins knocked by the next two balls. If a spare is picked up, the score for that frame is 10 points plus the number of pins knocked down with the next ball.
The 10th frame is a bit different from the preceding nine frames. If a player rolls a strike on the his first ball he can then another ball and, if necessary, try to pick up the spare. If he picks up a spare on his second ball, he then throws one more ball. If a player does not knock down all ten pins with the first two balls in the 10th frame, he does not get the opportunity for a third ball.