Sprinting with UserInputService isn't working?

Hi!

The issue with this script is that you attempt to index "char", which is a nil value since the Character doesn't exist yet. With player scripts like this, the script will run before the Character has loaded.

You are unable to use a WaitForChild() Instance since Character is a property of Player, not a child. So instead, you can use a Repeat Loop to wait until the Character has been loaded.

local player = game.Players.LocalPlayer
repeat wait() until player.Character --This will pause the script until the Character has successfully loaded.
local char = player.Character
local hum = char:WaitForChild("Humanoid")

local defaultws = hum.WalkSpeed

local uis = game:GetService("UserInputService")

function onKeyPress(input)
    if input.KeyCode == Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.RightShift then
        hum.WalkSpeed = 20
    end
end

function onKeyLeave(input)
    if input.KeyCode == Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.RightShift then
        hum.WalkSpeed = defaultws
    end
end

uis.InputBegan:connect(onKeyPress)
uis.InputEnded:connect(onKeyLeave)

Click "Accept Answer" if this was what you were looking for! Comment if you have any more concerns!

To solve this problem, you need to make sure that .Character is not nil.

To do this, you can simply add a repeat loop to make sure that the character is in the game!

So in conclusion, your code should look like this:

local player = game.Players.LocalPlayer

repeat wait() until player.Character -- Makes sure that the character is in the game.

local char = player.Character
local hum = char:WaitForChild("Humanoid")

local defaultws = hum.WalkSpeed

local uis = game:GetService("UserInputService")

function onKeyPress(input)
    if input.KeyCode == Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.RightShift then
        hum.WalkSpeed = 20
    end
end

function onKeyLeave(input)
    if input.KeyCode == Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.RightShift then
        hum.WalkSpeed = defaultws
    end
end

uis.InputBegan:connect(onKeyPress)
uis.InputEnded:connect(onKeyLeave)