In tenpin bowling, there are ten frames (not 12) per game. The
bowler has two shots per frame to knock all ten pins down. In the
tenth frame, if the bowler knocks all ten pins down in his first
shot (a strike), then he gets two more shots. These extra two shots
are called "fill balls." They are not extra frames (sometimes
erroneously referred to as the 11th and 12th frame).