Effect
Target 1 face-up monster on the field; equip this card to that target. It gains 500 ATK. If the equipped monster battles while in Defense Position, it gains DEF equal to its ATK during damage calculation only.
"After activation, this card becomes an Equip Card that increases the equipped monster's ATK by 500, and you equip it to 1 monster on the field" is the effect applied when the card "Chain Shield" is activated. (This effect targets 1 face-up monster in either player's Monster Zone.)
The "increases ATK by 500" effect is an effect applied to the equipped monster.
If you activate the card "Chain Shield" during the Damage Step, it must be activated from the start of the Damage Step up to before damage calculation.
The effect "If the equipped monster battles while in Defense Position, its DEF increases by its ATK only during damage calculation" is not an effect that starts a Chain. (It is an effect applied to the equipped monster.)
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