only seven games, because the first set of balls is also used for the pre-match warm-up. In ITF tournaments like Fed Cup, the balls are changed after every eleven games (rather than nine) with the first change occurring after only nine games (instead of seven). An exception is that a ball change may not take place at the beginning of a tiebreaker, in which case the ball change is delayed until the beginning of the second game of the next set. As a courtesy to the receiver, the server will often signal to the receiver before the first serve of the game in which new balls are used as a reminder that they are using new balls. Continuity of the balls' condition is considered part of the game, so if a re-warm-up is required after an extended break in play (usually due to rain), then the re-warm-up is done using a separate set of balls, and use of the match balls is resumed only when play resumes. On-court coaching A recent rule change is to allow coaching on court on a limited basis during a match. This has been introduced in women's tennis for WTA Tour events in 2009 and allows the player to request her coach once per set. Stance Stance refers to the way a player prepares themselves in order to best be able to return a shot. Essentially, it enables them to move quickly in order to achieve a particular stroke. There are four main stances in modern tennis: open, semi-open, closed, and neutral. All four stances involve the player crouching in some manner: as well as being a more efficient striking posture, it allows them to isometrically preload their muscles in order to play the stroke more dynamically. What stance is selected is strongly influenced by shot selection. A player may quickly alter their stance depending on the circumstances and the type of shot they intend to play. Any given stance also alters dramatically based upon the actual playing of the shot with dynamic movements and shifts of body weight occurring. Open stance This is the most common stance in tennis. The player's feet are placed parallel to the net. They may be pointing sideways, directly at the net or diagonally towards it. This stance allows for a high degree of torso rotation which can add significant power to the stroke. This process is sometimes likened