Limit the ability for managers to pick up and drop a player in the same fantasy day.
The reason for this rule (which we have as an unwritten rule in my league) is to prevent a manager from adding/dropping multiple players thereby putting a bunch of players on waivers so other managers can't pick them up. This way they have to keep their pick ups at least 1 fantasy day before dropping.

Hi,
If your league uses Continuous waivers, this behavior is expected as players are always on waivers with this setting. However, if you use standard waivers and a player is added as a free agent and dropped in the same day, they'll go back to free agency, not waivers.
We'll pass your feedback along to our team as well.
Thanks,
Yahoo Fantasy Support
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Yuri X commented
Would love to have this option as a setting so as commissioner I don't have to constantly monitor and admonish league mates for breaking the rule.