Backgammon Rule 101: An Illegal Move Rendition
There are four backgammon rules on how to move checkers correctly. One, we may only land on open points. Two, a dice roll represents two separate pip moves. Three, doublets represent four separate moves. And lastly, as long as rolls are in accordance with the abovementioned rules -- they must be used. Now, this fourth backgammon rule is all about observing what's called legal plays or legal checker movements. However, it's helpful to see an illegal move rendition that can come about which is, surprisingly, rather common during a live game.
One illegal move rendition is when either number at the cast of the dice is legal but both aren't allowed. An example is when you roll a six-four during a game and you can either move six pips or four pips but not both. In this case, if you use choose to advance four pips because it's much better to do so, then you've just made an illegal play.
The reason behind this is covered in a less-emphasized precept that's in accordance with the fourth backgammon rule. That is, if either number but not both numbers at the cast of the dice is available, we should always use the larger or higher number in stead of the lower one. That's why, from the example above, it's correct to use the six-pip move and not the four-pip move.
Another illegal move rendition deals with making a pip-move that results to making the other pip-move illegal. In accordance with the fourth rule, as long as pip moves at the cast of the dice are allowed, they must be used. Hence, if both moves are already allowed, given that they're played in a certain order, then we must carry them out. Otherwise, we'll be breaking this important backgammon rule
Let's say, you're in the process of bearing off. You have one piece each remaining on the four-point and three-point but there's two opposing pieces on your ace-point as well. You take your turn and roll a four-two. If you bear off from the four-point, you'll be making an illegal play because that will disable you from using the two-pip move for your three-point piece. Hence, the legal way to go about it is to move your four-point checker to the two-point and bear off your three-point piece.
After seeing some examples of an illegal move rendition, one might consider looking and observing each backgammon rule differently. Since there are many patterns of checker distribution in the game, questions about the legality of how to move checkers will always come about. So keep in mind that if either pip-move but not both are allowed, we are forced to use the higher number from the dice roll. Also, as long as both checker plays are permitted by a roll, we must use them in a particular order - if we must - so that we don't illegalize one when we opt for the other.