open season

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The period during which it is legal to hunt or catch certain game or fish.
• noun Informal A time of unrestrained activity, often criticism or harassment.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun hunting A period of time during the calendar year when authorities within a jurisdiction permit the unrestricted hunting of one or more kinds of animal wildlife.
• noun idiomatic A situation in which someone is endangered, blamed, harassed, or opposed in a sustained manner by a number of others; a situation in which something is endangered or otherwise opposed.
• noun idiomatic A situation in which or period of time during which some activity or circumstance routinely occurs.