In this rule

Historical Rules · 10 August 2018

Rule 506.3d

Official source text from the 10 August 2018 Rules release

Permalink

If an effect would put a creature onto the battlefield blocking but the creature it would block isn’t attacking either the first creature’s controller or a planeswalker that player controls, that creature does enter the battlefield, but it’s never considered to be a blocking creature.

Find this number in the current Rules