Assuming you are the better player, add extra opportunities for your friend to win. Here are some suggestions. Whichever one your buddy chooses, you have to follow one or more of these restrictions:
He wins when the 6, 7, 8, or 9 ball is made on a legal shot.
Last pocket - you win only if you sink the 9 ball in the pocket where you made the previous lower sequence ball.
When you are on the 9 ball for the first time, your buddy picks the pocket for the 9 ball that you must put it in order to win.
Friend picks 2 or 3 pockets on the table that you cannot sink balls in. If you do, the ball stays down, but you give up ball in hand.
Bank the nine one or more rails to win.
Friend gets ball in hand for every shot (or every other shot).
As the games progress, the rules can be modified to get the best equalization of skills. Using this type of handicapping (even when weighted against you), forces you to treat the game with proper attention.
Without this handicapping, you would not take the game seriously and thereby begin to play casually - not a good thing to do.
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