Historical clue formulations

• Baseball, colloquially — 2018-07-03
• Baseball, in America — 2017-04-04
• Baseball tag — 2015-04-02
• Source of pop-ups? — 2005-12-02
• Baseball ... with a hint to this puzzle's theme — 2003-08-18
• It's played at the 7-Down — 1994-05-06