scissors kick

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A movement in which the legs are moved widely apart and brought together like scissors, usually along the body's longitudinal axis, especially.
• noun A swimming kick having this form, used mainly in sidestroke.
• noun A bicycle kick in soccer.
• noun A midair kick in martial arts in which the feet are directed in different directions, especially to the sides.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a kick used in the sidestroke; legs are brought together in a scissoring motion