请看下面一段文字, 好像不仅仅是供初学者, 戴维斯杯也用. 加大尺寸,就是要累你的, 增加观赏性, 让球不太快, 不容易被打死(当然, 累死不管).

starshower (星雨)
In July 1999, the International Tennis Federation (ITF) announced an amendment to the Rules of Tennis allowing the use of an oversize tennis ball for all levels of play. Since the ruling, the oversized tennis ball has been used in Davis Cup and USTA play. Wilson has worked closely with the ITF and USTA to develop an oversize tennis ball that can be used in tournament play which provides longer rallies, more reaction time, and greater visibility
(#194036@0)
2001-9-8 -05:00

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