Situation: 

• At the end of player A's turn, the 5-ball is sitting on the lip of a corner pocket.
• Ten seconds later player B steps up to the table and tries to bank the 10-ball. Player B drills the 10-ball hard, and instead of the 10-ball going into the pocket it bounces back and forth between the side rail (neither the cue ball nor the 10-ball ever make contact with any other balls).
• At the end of that shot, the 5-ball has fallen into the pocket.

The 5-ball gets placed back as close to where it was before falling in the pocket and it is now player A's turn.

Once a ball has stopped all motion, it cannot move again without outside forces affecting it. Therefore, if a ball which has been hanging in a pocket for more than a few seconds suddenly drops, it is to be placed back on the table where it was originally sitting.

Rule: OTM page 48-49 section 7 "Pocketed Balls": https://media.poolplayers.com/TMRB/Team-Manual-English.pdf

Note: The debate over "outside forces" is usually the discussion around this rule in some cases. The APA HQ and SDAPA is if the ball (5-ball in this example) wasn't hit by another ball then it is considered outside forces that caused it to drop.

This section also covers:

• Balls that don't stay in the pocket
• Two frozen balls jammed in the pocket

You can submit a "Rule of the Week" to the league office:

• Email to sandiego@apaleagues.com.
• Email Subject Line must read “SDAPA Rule of the Week”
• Clearly state the rule/situation and if you know where the answer is found please provide those details.