Gin Rummy : Game Rules

In the online game of gin rummy, 10 cards each are dealt to 2 players. The 21-st card is opened face up and put next to the deck. This card is often referred to as upcard or up card. At each turn players draw a card by dragging it from either the closed deck or from upcard. When a player discards a card, the discarded card is placed on top of the current upcard so that the newly discarded card becomes a new upcard.

Only at the very start of gin-rummy game either player (starting with the non-dealer) gets a choice either to exchange one of the cards from their hands with an upcard or to select a Pass button to pass this opportunity. Before the 1st upcard is either passed or exchanged by both players, the rules of ginrummy do not yet allow any drawing from the closed deck. If the non-dealer elects to pass the 1st upcard, it would be the dealer's turn to consider exchanging the 1st upcard with one of the cards in hand or passing the 1st up card. Again, no drawing from deck is yet allowed.

If both of gin rummy online players refuse the very first upcard, the non-dealer must start a game by drawing the top card from the deck, add it to his hand and discard ANY card face up on top of the original upcard to continue the waste pile.

Thereafter, each player in turn must draw and add to his hand either the unknown top card from the deck OR the known upcard on the very top of the waste pile. In either case, the online player completes his turn by discarding one card face up to the waste pile. It is not permitted to draw the upcard & discard it on the same turn.

The melds that the player is building may consist of

1. either 3 or 4 cards of the same rank
2. sequence of 3 or more cards in the same suit (Ace & King are not considered consecutive, but Ace and 2 are ).

A hand consisting entirely of melds with no deadwood is described as gin and carries a bonus. The online player, however, does not have to wait for gin but may end up a game as soon as the total value of his unmatched deadwood is 10 or less. (This is called maximum knocking value. It is set at 10 for pure gin rummy. 

During online play melds are not revealed – they are kept secretly in hand.

Oklahoma Variation

While in regular Gin the knocking value is always 10, for the optional Oklahoma variation, that GameColony.com supports, the maximum knocking value can be lower than 10
The knocking value is determined by the value of the initial upcard. For example, such knocking value can be 2 if the initial upcard is 2. Initial Ace as an upcard, however, is a special case in Oklahoma -- the knocking can happen only with a Gin hand (0 points).
Oklahoma variation is sometimes played with a rarely used optional double-spades rule. This rule, however, is present in amateur games only as it diminishes the level of total required skill. Standard Oklahoma without double-spade rule is implemented at GameColony.com.

Knocking, Ginning and Laying-off

When an online player is satisfied with low value of his deadwood, he/she ends the game by ‘theoretically’ knocking on the table AFTER he/she has drawn an 11-th card and BEFORE discarding the last card [knock button]. The final discarded card is placed face up on the closed stock.

Knocking will be disallowed if the auto-calculated deadwood in knocker's hand will be greater than the maximum knocking value. After knocking, both the knocker and the opponent will see their cards on the table face up, arranged in melds. The opponent has the privilege of ‘laying off’ any cards of his own deadwood which may be matched with any of the knocker’s melds in order to reduce the penalty value of his deadwood. This privilege does not apply if the knocker has a gin hand with no deadwood. When both players' cards are shown, the opponent of the knocker can lay-off or attach his/her own deadwood cards to opponent's melds by dragging the cards towards opponent's ones. If a player has a gin hand, still the same 'Knock' button has to be pressed and the extra 11-th card has to be discarded. The system will determine automatically whether it was a gin hand or not.

If the knocker has the lower count of deadwood, he/she scores the the difference between their values of deadwood. For gin, the knocker adds a 25 point bonus.

If the knocker has higher or equal value of deadwood, the knocker receives a 25 point penalty for undercut plus any difference in deadwood values.

The 2 last cards of the deck may not be taken. If neither player has knocked before then, the deck is reshuffled.

The score is kept cumulatively for each player online. The winner adds his score for the hand to his previous total in order to make clear when 100 has been reached or exceeded. At GameColony.com 100 total points is a default, but players can choose 50, 100, 150, 200, 250, 300

The game ends as the player reaches the agreed upon number of points.

Finishing the hand and the 50-th card rule

The modern Tournament Gin Rummy rules add an extra detail to the situation when the stock pile is reduced to the last two cards. It is called the 50th card rule (the fiftieth card rule). If neither player knocks or gins and the 50th card is drawn from the stock pile, leaving two cards there, the 50-th card rule states that both players may have action on the 50th card. In other words, if one player draws the 50th card and doesn't knock, this player has to discard any open card to the discard pile. The opponent, then, will have the option either to take this open card and knock or pass (without taking this open card). If nobody uses the 50th card for knocking, the hand ends with a draw.

Here's a detailed description for the 50th card rule -- Modern Tournament Gin Rummy Rule:
To clarify, the 50th card rule relates to the situation when there are just 3 cards left in the closed stock and the hand is not over yet. Below is a step-by-step description of the game play and possibilities:

(1) Player A takes the 50th card and does not knock

(2) Player A discards some open card to a discard pile

(3) At this time, Player B has an extra "Pass" button that lights up. Player B also has a red 'guiding' message saying that it is possible to click the "Pass" button & draw this hand OR take this open card and knock

4) If Player B does not knock, he/she discards some card to a discard pile and the hand is finished in a draw

Auto-selection and player selection of melds at knocking

Unless a player uses 'Knocker Selects All Melds' table preference, in case of multiple melds, only the meld with the minimum points gets auto-selected. (Melds are shown as straight vertical or horizontal lines drawn on cards unless the option "Don't Mark Melds" is used.)
If a player knocks in a way where multiple meld-wise interpretations of the knock are possible, a player does not have to rely on computer auto-selection of melds. Instead, a player can select (even right before such knock) another Table Preference "knocker selects All Melds". With this option, the player will be in control of how to mark/select melds at knock time.