Dealer's Grip

Attack Reaction -

, destroy this: Target attack that has wagered gets +1

.

Battleworn

Rulings

From the Mastery Pack Warrior release notes

Dealer’s Grip’s first ability is a targeted effect: you must choose a target attack that has wagered when activating it. An attack that has not yet wagered at the time of activation is not a valid target.
An attack has wagered if a wager effect has been established and that wager’s result is dependent on that attack hitting or not.

Keyword notes

Battleworn - Equipment that wear down after each time they are used to defend. If you defend with a card with Battleworn, put a -1{d} counter on it when the combat chain closes.

When you defend with a card it remains on the combat chain until the chain closes, therefore you cannot defend with an equipment multiple times on the same combat chain.
A -1 counter stays on the card until the card is destroyed or the game ends.
If the defense of a card that is defending is below zero, its defense value is considered to be zero.
When this card is destroyed, it is sent to your graveyard. (Not when it has 0)
When this card is destroyed, it is sent to your graveyard.
If the defense of a card that is defending is below zero, calculate as if its defense is zero.