Modern tennis balls consist of an inner rubber core, filled with pressurised air, and a outer cover, made of wool or nylon, which is bound to the core by means of a heated press. According to the International Tennis Federation (ITF), when a tennis ball is dropped, vertically, onto a smooth, granite block from a height of 100”, or 8’4”, it should rebound to a height between 53” and 58”.
However, after a period of serious play – typically about three hours – the cover of a tennis ball may become fluffed up, so that the ball does not fly through the air as fast as a new one, and the ball may lose internal pressure, so that it does not bounce as high. Obviously, both these factors can adversely affect the control and accuracy of a tennis player, so tennis balls are routinely changed after every seven and nine games, alternately, throughout the course of a tennis match. The first ball change takes place after just seven games to allow for the warm-up. High humidity increases the moisture content of a tennis ball, and hence its mass, and high temperature can cause the ball to bounce higher, so ‘new’ balls are stored in a courtside refrigerator, maintained at a constant 68°F, or 20°C, to keep them in optimal condition.
The simple answer is yes, they are, but in a hierarchical structure, based entirely on ability, all tennis umpires start at the bottom of the profession. In Britain, to become a line umpire, or line judge – that is, a person responsible for calling a ball ‘In’ or ‘Out’ – they must pass basic training at the Lawn Tennis Association (LTA) before ‘running the line’ at local, county and regional tennis tournaments. A line umpire typically earns around £20,000 per annum.
However, for line umpires who excel, the LTA offers a further accreditation course, which includes a written examination on the Rules of Tennis, which introduces them to life as a chair umpire. Once accredited, in the professional game, chair umpires typically earn around £30,000 per annum, although at the higher end of the scale, a main umpire, or ‘designated official’, can earn upwards of £50,000 per annum.
Tennis umpires’ pay made the news in September, 2018, after a protracted argument between Serena Williams and chair umpire Carlos Ramos during her defeat by Naomi Osaka in the U.S. Open final. After a series of code violations, including calling Ramos ‘a liar’ and ‘a thief’ – for which she was later fined $17,000 – Williams still took home $1,850,000 in prize money; Ramos, one of the highest-rated chair umpires in professional tennis, received just $450, the daily rate paid by the United States Tennis Association (USTA).