The Major League Baseball rule book covers almost every imaginable situation that can occur in a game, including situations in which a batter or runner comes in contact with a batted ball. Whether the runner is out or allowed to advanced to the next base usually depends on the umpire's determination of whether contact with the ball was avoidable.
When the Runner Is Hit
If a batted ball hits a runner in fair territory, the umpire must determine whether or not contact with the ball was deliberate. If the umpire determines that the runner intentionally made contact with a batted ball or otherwise hindered a fielder from making a play on a batted ball, the runner is called out.
When the Batter Is Running
If a batter hits the ball into fair territory, he must run to first base. However, if he makes contact with the ball while running to first base before a fielder touches the ball, the batter is out. If the batter hits or bunts the ball and his bat hits the ball again in fair territory, the batter is also out.
Deflection by a Fielder
If a runner makes contact with a batted ball after the ball has been deflected by a fielder, the runner will not be called out. Likewise, if a ball gets by a fielder who could have made a play on the ball and the ball then hits a runner behind him, the runner will not be called out. However, if another fielder could make a play on the ball after it gets by the first fielder, the umpire may call the runner out for interference.
Runner Interference Calls
If a runner is called out for interference with a batted ball, the ball is considered dead, and play stops. No other runners may advance until the ball is returned to the pitcher and the umpire announces that play has resumed. A runner is also out if he interferes with a ball that is being thrown by a fielder who just made a play on a batted ball.