IDIOMS

open season

(idiomatic, often followed by on or for) A situation in which or period of time during which some activity or circumstance routinely occurs.

Example: 1912, Jack London, The Scarlet Plague, ch. 1:
  "But there weren't many crabs in those days," the old man wandered on. "They were fished out, and they were great delicacies. The open season was only a month long, too."
1919, William MacLeod Raine, A Man Four-Square, Prologue:
  In the country of the Clantons there was always an open season on any one of his name.
1964 March 20, "Patents: Knocking Down the Pole," Time:
  The court thus overruled all the states' protective laws, except against outright fraud, and declared open season on any products not protected by patents.
2009, "Tawny Weber," Coming on Strong, ISBN 9780373794669, p. 37:
  The paparazzi and gossip hounds have declared open season on celebrities.
1921, Peter B. Kyne, The Pride of Palomar, ch. 15:
  "My dear Miss Parker, this is the open season on terrible practical jokes."
1959 Oct. 26, "Music: Curtains Up!," Time:
  The open season on culture in Manhattan used to begin with the first stroke of a Metropolitan Opera baton.