A runner who is touching a base which he is entitled to occupy may not be tagged out. Runners may attempt to advance from base to base on any fair ball that touches the ground. When a ball is hit in the air (i.e., a
fly ball) and
caught by the defending team, runners must return and touch the base they occupy—called
tagging up—after the ball is first touched by a fielder. Once they do this, they may attempt to advance at their own risk. On a ball that touches the ground in fair territory, if there is a
force, runners are required to run. Base runners may attempt to advance at any time while the
ball is alive, even before or while the
pitcher is throwing a
pitch. The catcher—or pitcher, in lieu of delivering the pitch—often tries to prevent this by throwing the ball to one of the infielders in order to tag the runner. This
pick-off attempt is usually unsuccessful in tagging out the runner but is effective in keeping the runner closer to the base. If the runner is tagged out while diving back to the base, it is called a
pickoff. If the runner attempts to advance to the next base but is tagged out before reaching it safely, he is
caught stealing. A successful attempt by the runner is called a
stolen base. If a pitch gets away from the catcher, runners may also try to advance. This may be a
wild pitch, if the pitcher is held responsible for the ball getting away, or a
passed ball if the catcher is deemed to be at fault. Sometimes the defending team will ignore a runner who is trying to steal a base; in this case a runner is not credited with a steal, and the base is attributed to
defensive indifference. ==Strategy==