Yahtzees and Bonus Chips
A Yahtzee occurs when all five dice have the same value during one turn. Yahtzee is the most difficult combination to throw in a game and has the high score of 50 points. If a player scores one or more additional Yahtzees during the same game, that player is awarded bonus points and is given bonus chips that correspond to each additional Yahtzee that a player rolls. Bonus Yahtzees are worth 100 points each. Bonus chips are only awarded for subsequent Yahtzees if the first Yahtzee was placed in the 50-point Yahtzee score box. A player must still score in an empty box as per normal in addition to receiving the 100 point bonus.
Additional Yahtzees may be used as wild cards in the Lower Section (scoring full points in a lower section box, such as a long straight, despite not having the normally required dice) provided that the corresponding Upper Section box has been filled. For example, if a player rolled five threes (a Yahtzee in threes), the player could only use it as a wild card in the Lower Section if he or she already had a score in the Threes box in the Upper Section. If the Threes box was still open, the player must score 15 in the threes (sum of five threes).
In case a Yahtzee occurs after the Yahtzee box contains zero, the Bonus Yahtzee score is not awarded; but the wild card rule stated above still applies.
The original game rules released in 1956 contain a discrepancy in the rule above. The booklet stated that additional Yahtzees must be used as Jokers in the Lower Section and does not allow for their use in the Upper Section. However, the booklet also declares the highest possible score as 375, which would require the placement of Yahtzees in the Upper Section. This problem was corrected when the game was re-copyrighted in 1961.
Read more about this topic: Yahtzee, Rules Overview