... Anticipation

The use of anticipation prepares the audience for the next action about to occur and is generally only a couple of frames in length. Combined with exaggeration, in animation form, the motion is often more obvious however in real life movement there is anticipation e.g as a person goes to walk forward their body leans forward, as when a dancer is to jump off the floor, their knees bend first in preparation for the move.

In the example included of a baseball being thrown, the ball does not just leave the throwers mitt, his whole body moves in anticipation for the action, moving backwards then lunging forwards while his legs and hips move also before the ball has even left his hand.