Gin rummy

Gin rummy (or Gin for short) is a simple and popular card game created by E. T. Baker in 1909. Derived from knock rummy, Gin was created with the intention of being faster than normal rummy, but not as potentially spontaneous as knock rummy (in which a round could end before it really began.)

Play

Gin is played with a standard 52 card deck. Each player is dealt ten cards, one at a time. The rest of the deck is then placed face down between the two players, this is referred to as the stock. One card is taken from the top of the stock and placed face up next to it. The Non-dealer has the option of taking this upcard and discarding a card to put in its place. If the non-dealer chooses not to, the dealer has the same option. If the dealer also does not take the upcard, the dealer draws one card from the stock and discards a card, face up, atop the previous upcard.

Play continues in this manner; Each turn a player may either exchange one card for the discard pile or draw one card from the stock and discard from his hand. While a player may discard a card he has just received from the stock, he may not discard an upcard he has just taken. The player's primary goal is to create melds to score points. melds may consist of groups of three or four cards and sequences of three or more cards (in Gin, aces rank low.)

Unlike in standard rummy, but similar to knock rummy, melds are not laid out as soon as the player creates them, but rather when a player Knocks. A player may knock on his turn when the value of his deadwood (cards not included in a meld) are equal to or less than ten (10). When a player knocks, that player goes out and scoring commences for that hand. A player should indicate during his turn, before discarding, that he is knocking. He then discards and reveals his hand.

Scoring

Before scoring, the opponent of the knocker may lay off any of his deadwood onto the knocker's melds to lower his own deadwood count, so long as the card fits appropriately (i.e. an 8♥ on a meld of 8♠ 8♦ 8♣.)
Sometimes it is played that an opponent may not lay off deadwood if the knocker has gone gin, see below.

Scoring is as follows:

If the knocker's deadwood count is lower than his opponent's, the knocker wins the hand and scores points equal to the total of his opponent's deadwood, minus the total of his own. Aces being 1 and face cards being 10. If the knocker has no deadwood at all, he has gone gin and earns an additional 25 points.

If the total of the knocker's deadwood is equal or more than the opponent's deadwood count, then the opponent wins the hand and scores the difference of the knocker's deadwood with his own, plus an extra 25 points. This is called undercutting. The Knocker cannot be undercut if he has gone gin.

The game ends when one player has reached equal or more points than the set goal (typically 100). The player that reaches 100 points first earns a bonus of 100 points. If his opponent won no hands during the game. Both players earn 25 bonus points per hand they won during the game.