from NY Times

http://straightsets.blogs.nytimes.com/2009/09/11/the-importance-of-momentum-in-tennis/

The Importance of Momentum in Tennis

The match is a good example of the importance of momentum in a tennis match. In Chuck Kriese’s coaching bible “Total Tennis Training,” he describes why this invisible force is so important for a player to understand: “Tennis more than any other sport, is a game of momentum. The absence of a clock to do the dirty work of finishing off an opponent, and a scoring system based on units used makes the flow of the match much more important than any lead that has been established.”

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What can a player do when momentum shifts? Alistair Higham, a British tennis coach, has written a fascinating book on the subject. “Momentum, The Hidden Force in Tennis.” He believes that there are five distinct phases of momentum and that players can learn to recognize what stage they are in. At one end of the spectrum, momentum is totally against you, and Higham suggests slowing things down, being deliberate and following rituals. In baseball, when a pitcher is getting knocked around, the pitching coach strolls to the mound hoping to stall the rally. Timeouts in basketball are used for this reason as well.

When momentum is turning against you, Higham suggests increasing energy and playing more aggressively. When momentum is neutral, each player is vying to not only win points, but also to begin to control the momentum.