How can I access the physical player using a regular script?

I need to be able to access the physical player to change the humanoid of certain players without having them step on or click anything. I don't think it would work with a player added function either because it needs to happen in the middle of the game, but I could be wrong about this. I have tried to get the player name using local player, however that didn't work.

local players = game:GetService("Players")

while wait(1) do
	for i,v in pairs(players:GetPlayers()) do
		game.Workspace(v.Name).Humanoid.WalkSpeed = 20
	end
end

When using the script above this error message comes up: - Workspace.SeekingA:5: attempt to call a userdata value

And when using the script below it comes up with the same error message.

local players = game:GetService("Players")

while wait(1) do
	for i,v in pairs(players:GetPlayers()) do
		game.Workspace(players.Name).Humanoid.WalkSpeed = 20
	end
end

There are many different ways to do this, it just depends on what you're doing. Also, you cannot use game.Players.LocalPlayer in a server script, that only works in LocalScripts.

I fixed your script here:

local players = game:GetService("Players")

while wait(1) do
	for i,v in pairs(players:GetPlayers()) do
		if v.Character and v.Character:FindFirstChild('Humanoid') then
			v.Character.Humanoid.WalkSpeed = 20
		end
	end
end

You can also use this method, which will set a players WalkSpeed each time they respawn.

local players = game:GetService('Players')

players.PlayerAdded:Connect(function(plr)
	plr.CharacterAdded:Connect(function(char)
		repeat wait() until char and char:FindFirstChild('Humanoid')
		char.Humanoid.WalkSpeed = 20
	end)
end)