1. To throw a baseball when ready or at will. Often said as an imperative. We need to see what you're capable of, so pitch away whenever you're ready. He just stood there on the mound pitching away, one ball after another.

2. To discard something by throwing it away from oneself. In this usage, a noun or pronoun can be used between "pitch" and "away." The bear inspected the empty fast food container, then pitched it away with frustration. He pitched away the empty plate the moment he was finished.