Although each sanctioning body has their on rules you are typically limited to 2 bats when warming up in the on deck circle.
You are allowed 40 to 60 cards in your deck.
The maximum is 60 in the main deck.
there is no limit
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60, You can only have four cards with the same name in the deck.
A standard deck of playing cards typically contains 52 cards, with no specific limit on the number of "V cards" allowed.
In the official rules, a deck can have up to 4 EX cards.
In most trading card games, including Pokmon and Yu-Gi-Oh!, players are typically allowed to have up to 4 copies of a specific VMAX card in their deck.
It is currently now called the "Extra Deck", and a maximum of 15 cards (Fusion, Synchro, Xyz Monsters) are allowed.
According to the official rules of the game, a deck can have up to four artifact lands.
In the game, Magic: The Gathering, you can have up to four copies of a legendary creature card in your deck.
Technically they are not allowed to be outside the circle, but every on deck player usually does so. I have personally seen Derek Jeter, almost behind home-plate .near the stands to get a better look at the pitches. The umpires will allow this until it interferes with the flow of the game, then they will not allow it anymore.