this is in a server script not a local script the reason because they can change their client Side.
my server script that gets fired on character added
game.Players.PlayerAdded:Connect(function(plr)
plr.CharacterAdded:Connect(function(char)
Hum = char:WaitForChild('Humanoid')
if Hum then
Hum:ChangeState('Ragdoll')
end
end)
end)

4 comments
Unsure but I don't think Ragdoll works on R15 characters without making a custom one.
this would ragdoll as soon as the player joins and then not anymore
you should probably add something you click in order to ragdoll
this probably has something to do with FE ? usually when i make scripts they are interrupted by the FE update