A swinger is a tool used in horse racing to aid in the starting of races. It consists of a metal arm attached to a post that swings across the starting gate. When the starting gate opens, the swinger swings across the gate, striking the horses on the hindquarters and encouraging them to move forward. The swinger helps to ensure that all horses are given a fair chance to start the race at the same time. It is an important piece of equipment in horse racing and helps to ensure the safety and fairness of the sport.