Plausible movement needs space

'Sunday morning drive'. To make a picture with motion plausible, have somewhere for the moving object to go. Click image to view large.

No space to move into? Suddenly the picture looks static despite motion blur.
The second picture has become static compared to the first. Cropping it appears to have taken the motion out of the picture. With no space for a moving object to move forward the way the eye sees the picture changes. Somehow it loses its character.
In movement and action shots the space that surrounds the moving object is important. Try to provide some context. In order for the eye and brain to interpret the movement our imagination follows the implied line of the movement. Deny the eye a line of movement and that relationship disappears.
In truly dangerous situations it is the fear of what will come next that creates the energy and fascination of the action. If you sacrifice the space in your image where the action will happen next you also sacrifice the anticipation that makes the shot. All high-stakes action shots rely on the imagination to create an atmosphere of expectation or impending doom. Look for that and bring it out in your pictures.
All movement needs somewhere to go. Help the eye to follow an implied line that will take the moving object forward. Give the imagination somewhere for the next instant to happen. Your movement will be much more dynamic and your viewer much more involved.
Cropping
implied line
Getting Started With Action Shots
Space To Move Into… Action Needs Space
The Danger in Action Shots
Action Panning Shots with Motion Blur
Practicing and Improving your Panning
Panning With Motion… Look For A Compelling Background
Composition – resources pages