When I was typing I thought it was completely simple, but when I looked at it as I got the error I just couldn't figure out. I just thought I would put Speed.Value as game.Players.LocalPlayers.Character.Humanoid.WalkSpeed. Any way this is what I had.
game.Players.PlayerAdded:Connect(function(player)
local leaderstats = Instance.new("Folder")
leaderstats.Name = "leaderstats"
leaderstats.Parent = player
local plr = game.Players.LocalPlayer.Character.Humanoid
local speed = Instance.new("NumberValue")
speed.Name = "Speed"
speed.Parent = leaderstats
speed.Value = plr.WalkSpeed
end)

9 comments
What are you saying I should do with the player.Character.Humanoid.WalkSpeed?
I would recommend using :GetPropertyChangelSignal() to do this.
And don't you need to express humanoid by doing game.Player etc.
Not if you already have the player expressed
in your leaderboard use the player.Character.Humanoid.WalkSpeed to set it by default
Where would I put player.Character.Humanoid.WalkSpeed
nvm
Its saying Humanoid is a (nil value)
infact have the leaderstat script set it to 16 be default