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.
59
there is no limit
60, You can only have four cards with the same name in the deck.
It is currently now called the "Extra Deck", and a maximum of 15 cards (Fusion, Synchro, Xyz Monsters) are allowed.
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.
You can have up to 3 copies of each card of the Crystal Beast series in your Deck. There is no limit to the amount of Crystal Beast cards you can have in a Deck.
four positions are allowed into the semi circle also known as the "D" or "goal circle". those positions are GD (goal defense) GA (goal attack) GK (goal keeper) and GS (goal shooter)
In the Anime, no character ever has any more or less than forty cards in their deck. In real life, you can have up to sixty, but the minimum is forty.
how many clubs are in a deck of 52.
There is no hard limit. You can use a 100% artifact deck if you wish. It might not necessarily be viable depending on format, but there are some artifact land, and some 0-cost artifacts that produce mana.