It can vary in size from that of a softball to that of a soccer ball, and is made out of anything from cloth to hard rubber. However, most dodgeballs are roughly the size of a volleyball and composed of foam with a thin plastic shell. Some leagues allow the use of multiple sizes of dodgeballs in a single match (often with restrictions on whether men or women can throw certain sizes), while others use one standard size for all balls.
When the referee blows the opening whistle, players may rush to pick up the dodgeballs on their own attack line (or, if the balls are on the centerline, the balls to the right of center court). Some leagues allow players to pick up any ball, regardless of location. Players may only begin to throw at the opponents once a ball has been brought back over the endline.
Source: Wikipedia > Dodgeball
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