this is from onepocket.org rules
bolded and enlarged for emphasisis
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9. Spotting balls
9.1 Balls spotted on foot string: Balls are to be spotted on the foot spot, or in a direct line below the foot spot in the nearest available opening. Spotted balls shall be tightly frozen to other object balls that fall in or interfere with that line, without dislodging interfering balls. However if the cue ball interferes, the spotted ball is to be placed on that line close to, but not quite frozen to the cue ball. In the event that the line below the foot spot is full and the bottom rail interferes with a spotted ball then balls are to be spotted on the same line, but above the foot spot.