Call It Quits Meaning

(idiomatic) To conclude; to quit or stop an activity, especially after applying oneself to it for a significant period of time.

Example: 1909, Jack London, Martin Eden, ch. 15:
  One afternoon, after twenty minutes of desperate efforts to annihilate each other according to set rules that did not permit kicking, striking below the belt, nor hitting when one was down, Cheese-Face, panting for breath and reeling, offered to call it quits.
1992 May 11, "A One-Two Punch Rattles Germany," Time:
  The West's longest-serving foreign minister called it quits last week.