raring to go
Very eager to begin, as in The children were all dressed and raring to go. This idiom uses raring for rearing, and alludes to a horse's standing on its hind legs when it is anxious to get moving. [Early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.