The fielder at the front of the line then becomes the batter. If the batter hits a line drive or pop-up to the fielders, whoever catches the ball, regardless of their position in the line, becomes the new batter; the batter moves to the end of the line.
When the player at the head of the lineup becomes the batter, if they hit a line drive or pop-up that is caught by any fielder, that fielder becomes the new batter. The original batter then shifts to the back of the lineup.