pit against

Set in direct opposition or competition, as in The civil war pitted brother against brother. This idiom alludes to setting fighting cocks or dogs against one another in a pit. [Mid-1700s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.