The answer to this question is somewhat complicated, as there are a number of legal and illegal methods that can be used to count cards in blackjack. Generally speaking, however, it is illegal to use any method that could give an advantage to the player.
One common method of counting cards is to use a single card as a guide. This is generally considered legal, as long as the card is not shown to the player or other players.
Other methods that are generally considered illegal include peeking at the card before it is played, counting the number of spots above or below the dealt card, or using any other form of communication with other players. .
As long as players are abiding by the rules of blackjack, there is no issue with counting cards. However, if players are using methods that give them an unfair advantage, they may be breaking the law.
So, while it is technically legal to count cards in blackjack, it is always best to play cautiously and avoid any methods that could give you an advantage over your opponents.
