<Dd> A throw - off takes place from the center of the court . The thrower must touch the middle line with one foot, and all the other offensive players must stay in their half until the referee restarts the game . The defending players must keep a distance of at least three meters from the thrower until the ball leaves his hand . A throw - off occurs at the beginning of each period and after the opposing team scores a goal . It must be cleared by the referees . </Dd> <Dl> <Dd> Modern handball introduced the "fast throw - off" concept; i.e., the play will be immediately restarted by the referees as soon as the executing team fulfills its requirements . Many teams leverage this rule to score easy goals before the opposition has time to form a stable defense line . </Dd> </Dl> <Dd> Modern handball introduced the "fast throw - off" concept; i.e., the play will be immediately restarted by the referees as soon as the executing team fulfills its requirements . Many teams leverage this rule to score easy goals before the opposition has time to form a stable defense line . </Dd> <Dl> <Dt> Throw - in </Dt> <Dd> The team which did not touch the ball last is awarded a throw - in when the ball fully crosses the side line or touches the ceiling . If the ball crosses the outer goal line, a throw - in is awarded only if the defending field players touched the ball last . Execution requires the thrower to place one foot on the nearest outer line to the cause . All defending players must keep a distance of three metres (9.8 ft). However, they are allowed to stand immediately outside their own goal area even when the distance is less than three meters . </Dd> </Dl>

Write a short note on the ball used in the game of handball