Shuffle one deck of cards and deal out the entire deck between you and the other player. Each person places down their cards in five piles like in Solitaire (top card face up, each pile with increasing numbers of cards). These piles are called 'stock piles'. Your first pile is one card face up, the second is one face down and one face up and so on to the fifth pile which is four face down and one face up. Each player should end up with 11 cards in their hand. These should not be looked at and should be placed face down between the player and their 5 stock piles. The 11 cards are called the 'draw piles' or 'spit cards'. Enough room should be left between both players' stock piles for two additional piles of cards. These piles are the 'spit piles' (not to be confused with 'spit cards') and will be discussed next.
To begin a round, both player say "Spit" and each turns over one card from their draw piles and places them side by side between their stock piles. These cards are the beginning of the 'spit piles'. From here it becomes a race. Players attempt to get rid of all the cards in their stock piles by placing cards in numerical order up or down on the spit piles. For example, a 3 can be played on either a 2 or a 4. Suit and color don't matter in this basic version. Cards can wrap around so that aces can be played on twos or kings.
Cards can only be played from the stock piles. However, if there is an empty space where a stock pile used to be, a card from another stock pile can be moved to that space. If a card on top of a stock pile is face down, you can turn it over and try to play it. You should never have more that 5 stock piles.
If at any point you can't play a card from your stock piles, you must wait until your opponent cannot play as well. When this happens you "spit" again (most players actually say "Spit" when they turn over the cards) and each player turns over a card from the draw piles onto the spit piles. If a player has no draw pile cards then the other player spits alone and can choose the pile on which he places the card. This cycle of playing and spitting continues until one player is out of cards in their stock piles. The round is over when this happens and players slap the pile they think has fewer cards. Whoever get there last has to take the other pile. If you have any stock pile cards left over, they should be added to the piles you just picked up and to any draw pile cards you have and then reshuffled. Five more stock piles are laid out and round two begins.
After several rounds, one player will most likely have less than 15 cards left and therefore will not be able to have 5 complete stock piles and a draw pile. When this happens they should build as many complete stock piles as possible but will not spit at the beginning of the round. This means that there will only be one spit pile in the middle. Play continues as usual with the player with the draw pile spitting alone when he/she can't play. The loser of the round takes all the cards. The winner takes none.
To play a shorter version follow these rules. Ten cards should be placed face down on the table between players in this order: 5 cards, 1 card, 1 card, 5 cards. The two piles of 5 cards are called 'spit cards'. The two piles with only one card are called the 'spit piles'. The rest of the deck should be divided equally between both players. Each player should place these cards face down easily within reach. This is your draw pile. Each player then takes four cards from their draw pile. This is your hand. You can only have four cards in your hand at any time. Both players turn over the two single cards in the middle to start the spit piles and thus start the game. Then each player proceeds to play cards on the spit piles from your hand according to the normal rules of "Spit" stated above. As you play cards from your hand you replenish cards from your draw pile. The first person to play all the cards in their hand and draw pile wins. If both players cannot play, they can "spit" from the two piles of 5 cards (the spit cards) on either side. If players 'spit' they must do this at the same time. If you run out of spit cards then you flip the spit piles over and they become spit cards. Then two new spit piles should be formed by taking one card from the top of each spit card pile.