<P> Conversely, because the four - seamer doesn't break, it is quite hittable by the quick, "good - eye" batter who can "see" where the pitch will arrive . Moreover, its extreme velocity helps experienced batters to hit it extremely hard; that is, if a batter can "square up" on it, a four - seamer pitch can be readily hit for power . Further, a fastball's effectiveness decreases substantially if it is not accurately thrown, i.e., if the pitch is not under control . Due to its straight and level flight an errant fastball will not fool many batters as to its direction; thus, it elicits fewer swings and produces more walks when thrown outside the strike zone . As a pitcher's fastball loses "heat" (speed), more batters will have sufficient time to read and hit the pitch . </P> <P> Pitching or throwing a fastball "comes naturally" to most athletes who throw baseballs . The fastball is typically one of the first pitches taught to young pitchers . It requires very little unnatural motion of the arm, elbow or shoulders, and the ball comes off the fingers easily when the pitch is completed as it is intended to be thrown . The fastball is the most common of pitches, as almost all pitchers throw a fastball as part of their standard repertoire . </P> <P> Scientific studies have shown that the four - seam and two - seam fastballs have essentially the same flight paths and speeds, but, typically, a batter perceives a difference between them . The perceived difference is due to flicker fusion threshold, which is defined as the frequency that a flashing light appears "steady" to the human eye . For example, for a series of flashed still - pictures to appear steady, the frequency of flashing has to be at a rate greater than the flicker fusion threshold, which for humans is about 60 Hz, or 60 cycles per second . </P> <P> A major league pitcher throws a baseball with a spin of around 20 rotations per second (rps). With each rotation, a four - seam fastball presents four seams crossing the vision of the batter, producing a flicker rate of 80 Hz, which results in the batter not perceiving any features on the ball and having fewer visual cues than with the two - seamer to track it . Thus, the batter often perceives the four - seam fastball as faster and higher than a two - seam fastball . </P>

What is the difference between two seam and four seam fastball