2
general::
Phrase(s): give free rein to someone [and] give someone free rein
Fig. to allow someone to be completely in charge (of something). (Alludes to loosening the reins of a horse and therefore control.) • The boss gave the manager free rein with the new project. • The principal gave free rein to Mrs. Brown in her classes.
McGrawhill's American Idioms And Phrasal Verbs