How can I change a player's walkspeed when they say something in chat?

I have scripted the word, but it wont change the player's speed. The script is here:

local GroupId = 8983096 local MinimumRank = 5

local animation = Instance.new("Animation") animation.AnimationId = "http://www.roblox.com/Asset?ID=6484830111"

game.Players.PlayerAdded:Connect(function(Player) Player.Chatted:connect(function(Message) if Player:GetRankInGroup(GroupId) >= MinimumRank then if Message == "Speed" then local animTrack = Player.Character.Humanoid:LoadAnimation(animation) animTrack:Play()

       end 
    end
end)

end)

local GroupId = 8983096 local MinimumRank = 5 local plr = game.Players.LocalPlayer

game.Players.PlayerAdded:Connect(function(Player) Player.Chatted:Connect(function(Message) if Player:GetRankInGroup(GroupId) >= MinimumRank then if Message == "Speed" then game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 25 end end end) end)