When will a MLB umpire call a delay of game?

Answer 1

The home team is in charge of determining whether the game starts on time due to rain. When the managers meet with the umpires at home plate before the game, the umpires are then in charge.

Below are snippets from MLB Rule 4.01:

"Unless the home club shall have given previous notice that the game has been postponed or will be delayed in starting, the umpire, or umpires, shall enter the playing field five minutes before the hour set for the game to begin and proceed directly to home base where they shall be met by the managers of the opposing teams."

"As soon as the home team's batting order is handed to the umpire-in-chief the umpires are in charge of the playing field and from that moment they shall have sole authority to determine when a game shall be called, suspended or resumed on account of weather or the condition of the playing field."