The following is largely derived from the chapter on pitching from Leonard Koppett’s “The Thinking Fan’s Guide To Baseball.”
A fastball is essentially straight, although it does have a little movement to it (what the commentators call a “live” fastball).
A curveball breaks down and away from a hitter of the same-handedness as the pitcher.
A changeup is a pitch that is significantly slower than usual. As a pitcher, you are trying to get the hitter to think you’re throwing a fastball, and thereby swing the bat far too early. A “straight change” is a changeup that travels the same basic path as a fastball. Some pitchers use their curveballs as their change-of-pace pitch.
A slider moves a little bit left or right, but not much up or down.
A sinker moves down, but not really left or right.
A screwball is a very rare pitch. It acts as a reverse curve, breaking down and in toward a hitter of the same-handedness as the pitcher. It puts a lot of strain on the arm, however.
A knuckleball is thrown with no spin, causing it to be randomly affected by the air. It’s so easy to throw, you can be a good knuckleballer well into your 40s.
A split-fingered fastball drops.
A spitball – or Vaseline ball or K-Y ball or whatever – will drop. For more information about these pitches, read up on Gaylord Perry, evil master of pitches involving illegal stuff.
Let me just add that there’s no such pitch as a breaking ball – that term refers to any kind of pitch that breaks. I must confess, I managed to make it into my mid-20s before I realized this fact. I always wanted to know what the grip of a “breaking ball” was.