Historical Rules · 8 March 2024
Rule 509.7a
Official source text from the 8 March 2024 Rules release
If the effect that puts a creature onto the battlefield blocking specifies it’s blocking a certain creature and that creature is no longer attacking, the creature is put onto the battlefield but is never considered a blocking creature. The same is true if the controller of the creature that’s put onto the battlefield blocking isn’t a defending player for the specified attacking creature.