Zerozerock

The effect "While this card is face-up on the field, your opponent cannot select a face-up Attack Position monster with 0 ATK as an attack target" is an effect that does not create a Chain Link.

The effect of "Zerozerock" applies not only to monsters that were on the field when the card was activated, but also to monsters that are Summoned to the field afterward, making it so that "your opponent cannot select a face-up Attack Position monster with 0 ATK as an attack target."

If a monster with 0 ATK in face-up Defense Position is selected as an attack target, and then becomes face-up Attack Position due to the effect of a card activated during the Battle Step, the "Zerozerock" effect is not applied because it has already been selected as an attack target.