local Stamina = 100

​

local SprintHeld = false

local Sprinting = false

local Exhausted = false

​

local RunRefresh = 20 -- when to allow running after exhausted

local SpeedDiff = 6

local DrainRate = 20 -- drain per second

​

local function sprint(active)

    if Exhausted then return end -- we can't run because we're exhausted!

    if active then

        Humanoid.WalkSpeed = Humanoid.WalkSpeed + SpeedDiff

    else

        Humanoid.WalkSpeed = Humanoid.WalkSpeed - SpeedDiff

    end

    Sprinting = active

end

​

UserInputService.InputBegan:Connect(function(input)

    if input.KeyCode ~= Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.ButtonR2 then return end

    SprintHeld = true

    sprint(SprintHeld)

end)

​

UserInputService.InputEnded:Connect(function(input)

    if input.KeyCode ~= Enum.KeyCode.LeftShift or input.KeyCode == Enum.KeyCode.ButtonR2 then return end

    SprintHeld = false

    sprint(SprintHeld)

end)

​

RunService.Heartbeat:Connect(function(DeltaTime)

    if Sprinting then

        if Stamina > 0 then

            Stamina = Stamina - DrainRate * DeltaTime

        else

            sprint(false)

            Exhausted = true

        end

    elseif Stamina < 100 then

        Stamina = Stamina + DrainRate * DeltaTime

        if Stamina > RunRefresh then -- we can now run again!

            Exhausted = false

            if SprintHeld then -- resume running because player is still holding down the sprint key!

                sprint(SprintHeld)

            end

        end

    end

end)