US Open-Hindrance Rule

The hindrance rule that chair umpire Eva Asderaki used to dock Serena Williams a point Sunday in her U.S. Open final loss to Sam Stosur:

26. HINDRANCE

If a player is hindered in playing the point by a deliberate act of the opponent(s), the player shall win the point.

However, the point shall be replayed if a player is hindered in playing the point by either an unintentional act of the opponent(s), or something outside the player's own control (not including a permanent fixture).