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.
Slang Impulsively whimsical; eccentric: That screwball proposal won't work.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.