Definitions for "Fair ball"
(baseball) a ball struck with the bat so that it stays between the lines (the foul lines) that define the width of the playing field
a ball delivered by the Pitcher while standing in his position, and facing the Batsman, the ball so delivered to pass over the Home Base, not lower than the Batsman's knee, nor higher than his shoulder
a ball that lands in fair territory between home and first base, home and third base, is on or over fair territory when bounding toward the outfield, touches first or third base, or first falls on fair ground beyond first or third base