ˈopen ˌseason noun [singular, uncountable]

1. British English the time each year when it is legal to kill particular animals, birds, or fish as a sport Antonym : close season
open season for
the open season for deer

2. open season (on somebody) a time when a lot of people criticize someone, or a group of people:
It seems to be open season on politicians just now.

[TahlilGaran] Dictionary of Contemporary English ▲

open season
open season (on (someone/something))
a situation in which someone or something is criticized or treated unfairly.
City newspapers have declared open season on the mayor.

She feels it's almost like someone has declared open season on anyone who looks like a foreigner.

Etymology: based on the literal meaning of open season (= the time of year when hunting is legal)
a period of time when people criticize or unfairly treat a particular person or group of people.
With the publication of these two reports, it seems to be open season again on single mothers.
(often + on)
Newspaper editors have declared open season on the royal family.

[TahlilGaran] English Idioms Dictionary ▲