Be eager for, as in He's just spoiling for a fight. This idiom nearly always refers to some kind of altercation. It may allude to spoil in the sense of “deteriorate over a period of time.” [Mid-1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.