Someone or something that expels saliva from the mouth, or in baseball, a type of illegal pitch where the ball is treated with moisture.
From 'spit' (Old English 'spittan') plus the agent suffix '-er.' The baseball sense emerged in the early 1900s when pitchers discovered that water or saliva on the ball made it move unpredictably.
The spitball was banned from baseball in 1920, but pitchers had used it for decades—it's one of the few things so unfair that sports had to literally make it illegal!
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