to leave the field free: to put up no opposition; to refrain from entering into competition; to allow something or someone to proceed unhindered or…

to let (or leave) well alone: to refrain from trying to make better that which is already satisfactory. Also to let (or leave) well enough alone.

to get out of a person's face (and variants): to leave a person alone, stop bothering a person (usually in imperative).

intransitive. To refrain from intervening. Usually ironically: to intervene.