Movement. Because it goes vertically and has no horizontal break, the 12 to 6 curveball is the most difficult to hit. If a pitcher uses a fastball correctly in a throwing sequence, the difference in speed and break makes the pitch tough to hit. However, if a hitter sees the ball well, he can adjust his stance or use a swing change to deal with this type of pitch. The harder the ball is thrown, the more force is applied to the ball's surface. This creates friction that allows the ball to roll more when it hits the ground. A low-velocity ball tends to skid across the grass rather than rise up high because there is less friction at play. A high-velocity ball will keep its shape better as it travels through the air. Breaking balls are classified by how much side-to-side movement they have: 0-15 degrees for flatters, 15-30 for hooks, and more than 30 for sliders. Although all three types of breaking balls are difficult to hit, some pitchers have their own specialty - which helps them decide when to use which one during games. For example, a pitcher might mix in a few slider pitches here and there to wear down an opponent. It's also helpful when trying to figure out how to hit a particular pitch to know the type of move the pitcher uses to create it.