When the Rockies hosted the Reds, May 13, 2021, Reds' pitcher, Luis Castillo, did something funny. He stepped backwards (legally) off the pitching rubber and then delivered a pitch to the plate. Since no runner was attempting to steal home, it was an illegal pitch, which is a balk with runner(s) on base.

Read all about it:

https://baseballrulesacademy.com/reds-pitcher-steps-off-rubber-and-delivers-a-pitch-is-that-legal/