E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Shoe the Wild Colt (To).
To exact a fine called footing from a newcomer, who is called the colt. Colt is a common synonym for a greenhorn, or a youth not broken in. Thus Shakespeare saysAy, thats a colt indeed, for he doth nothing but talk of his horse. (Merchant of Venice, i. 2.)