- Baseball a ball thrown by a right-handed pitcher that curves to the right, or one thrown by a left-handed pitcher that curves to the left
- Slang a person who seems erratic, irrational, unconventional, or unbalanced
- Baseball A pitched ball that curves in the direction opposite to that of a normal curve ball.
- Slang An eccentric, impulsively whimsical, or irrational person.
- (baseball) A pitch thrown with added pressure by the index finger and a twisting wrist motion resulting in a motion to the right when thrown by a right-handed pitcher.
- The screwball is not thrown much because it tends to damage pitcher's arms.
- (US) One who behaves in a crazy manner.
- I will not listen to this screwball any longer.
(comparative more screwball, superlative most screwball)