Fielders have a right to occupy any space needed to catch or field a batted ball and also must not be hindered while attempting to field a thrown ball.
If any member of the batting team (including the coaches) interferes with a fielder's right of way to field a batted ball, the batter shall be declared out. If any member of the batting team (including the coaches) interferes with a fielder's right of way to field a thrown ball, the runner on whom the play is being made shall be ruled out. In both cases, the ball will be declared dead and all runners must return to their last legally occupied base at the time of the interference. However, a runner is not obligated to vacate a base he is legally permitted to occupy to allow a defender the space to field a batted or thrown ball in the proximity of said base.
Interference can also be called on the offensive team if a batter hinders the catcher after a third strike when the ball is not caught, a batter intentionally deflects any foul ball, and a baserunner hinders a following play being made on another runner after having scored or been put out. When running the last half of the way to first base while the ball is being fielded in the vicinity of first, a baserunner must stay within the three-foot runner's lane to the right of the foul line unless they are avoiding a player fielding a batted ball. If the umpire determines that the baserunner has interfered with the player taking the throw at first base by running to the left of the foul line or to the right of the runner's lane, the baserunner can be called for interference.
Watch: Jacoby Ellsbury is called for interference after bumping into Alexei Ramirez, who was in the process of fielding a ball.