What is the rarest play or occurrence in major league baseball.?

This came up in a discussion in one of my leagues. One member said the unassisted triple play since it has occurred just 15 times on MLB history. Others said a triple play without a ball touching a bat, a triple play in which the batter wasn't one of the outs, and hitting a grand slam in the first major league... show more This came up in a discussion in one of my leagues. One member said the unassisted triple play since it has occurred just 15 times on MLB history.
Others said a triple play without a ball touching a bat, a triple play in which the batter wasn't one of the outs, and hitting a grand slam in the first major league at bat.
It looks like the grand slam in the first at bat has happened 6 times but I'm not sure about the others.

I say it is hitting for the home run cycle as it has never occurred at the major league level; Ty Horn did it in AA ball back in 1998.

What do you think is the rarest play?
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