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This code goes in a LocalScript inside StarterPlayerScripts

--// Services
local UserInputService = game:GetService('UserInputService')
local ReplicatedStorage = game:GetService('ReplicatedStorage')
local Players = game:GetService('Players')

--// Debounces
local Punching = false
local Damaging = true

--// Customisation
local Damage = inf
local Cooldown = 0.2

--// Events
local PunchEvent = ReplicatedStorage:WaitForChild('PunchEvent')

--// Player
local Player = game.Players.LocalPlayer
local Character = game.Workspace:WaitForChild(Player.Name)
local Humanoid = Character:FindFirstChildOfClass('Humanoid')
local RightArm = Character:WaitForChild('Right Arm')

--//Animations
Punch = Instance.new('Animation')
Punch.AnimationId = 'rbxassetid://953446258'
PunchTrack = Humanoid:LoadAnimation(Punch)

--// Coding
UserInputService.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.E and not Punching then
        Punching = true
        PunchTrack:Play()
        PunchTrack.KeyframeReached:Connect(function(Keyframe)
            if Keyframe == 'End' then
                wait(Cooldown)
                Punching = false
                Damaging = true
            end
        end)
    end
end)

RightArm.Touched:Connect(function(hitPart)
    if Punching and hitPart.Parent:FindFirstChild('Humanoid') and Damaging then
        Damaging = false
        local HumanoidToDamage = hitPart.Parent:FindFirstChild('Humanoid')
        PunchEvent:FireServer(HumanoidToDamage, Damage)
    end
end)

This code goes inside a Script inside ServerScriptService

--// Services
local ReplicatedStorage = game:GetService('ReplicatedStorage')

--// Events
local PunchEvent = ReplicatedStorage:WaitForChild('PunchEvent')

--// Coding
PunchEvent.OnServerEvent:Connect(function(PlayerWhoSent, HumanoidToDamage, Damage)
    HumanoidToDamage:TakeDamage(Damage)
end)

Make sure you create a RemoteEvent called 'PunchEvent' and parent it to the ReplicatedStorage