Lock down players once the game kickoff starts
Yahoo needs to lock players once the game begins
Last night a player in our league was able to pick up Likely during
the fourth quarter. Commissioner set can't drop benched players once
the game starts but user was still able to pick up Isaiah Likely during the game last night, been fighting this problem for 15+ years. Its simple once the game starts every player for those 2 teams gets locked for waiver pickups for next week.

Hi,
It sounds like your league uses no waivers, which means players are never on waivers and can be added as free agents at any time.
The commissioner of your league can manually drop players via the Commissioner tab --> Manage Other Teams tab --> Edit Rosters.
Thanks,
Your friends at Yahoo Fantasy
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Dennis McCarthy commented
Please lock players once kickoff happens for those teams