<P> A related rule called the intentional drop rule (Rule 5.09 (a) (12)) applies even when second base is unoccupied, and applies even when the batted ball is a line drive or a bunt that could be caught on the fly . This rule likewise prevents a fielder from deliberately dropping a ball and thereby achieving a double or triple play . If an umpire invokes this rule, the drop is ruled a catch, the ball is dead, and no baserunner may advance . The rule is not invoked when a fielder plays a ball on a bounce that might have been caught on the fly . </P> <P> For the runners, an infield fly is little different from an ordinary fly ball . If an infield fly is caught, the runners must retouch their original bases ("tag up") after the catch before attempting to advance . If an infield fly is not caught, no tag up is required and the runners may advance at their own risk . The only difference is that the umpire's declaration that the batter is out removes force plays and gives runners the option of staying on the base . </P> <P> The infield fly rule states that runners may advance "after the ball is touched". This rule governs the tag up if the infield fly is caught . The runner does not need to wait on base until the fielder achieves full control of the ball . There is no need to tag up at any time if the ball is dropped . There is no concept of tagging up under the intentional drop rule, as base advances are not allowed . </P> <P> A runner hit by an infield fly while standing on a base is also protected from being declared out due to interference, unless this interference is deemed intentional (which appeared in the rules in 1940). </P>

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