Works in studio but How do I get this to work in real game?

The :GetMouse() Function only works in localscripts, if it is in one already, check any errors with the Player variable. | If this was the answer, please mark it as the answer so I can get more reputation so I can help others as well. [Edited Below]

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The script also uses only R15 so it will not have any effect on R6 users.

I have fixed your line of code as well:

plr = game.Players.LocalPlayer
local z = plr:GetMouse()
loaded = false
plr.CharacterAdded:connect(function() --This triggers the loaded function to become true when character has loaded
	loaded = true
end)

repeat wait() until loaded == true -- This will wait and prevent any functions below from running until the loaded variable becomes true

plr.Character.Humanoid.Died:Connect(function() -- Changes variable back to false so it can restart the script.
	loaded = false
end)

z.Button1Down:connect(function()
	if loaded == true then -- This also makes sure the character is loaded before anything
local v = Instance.new("BodyVelocity")
v.MaxForce = Vector3.new(math.huge, math.huge, math.huge)
v.Velocity = z.hit.lookVector * 100
v.Parent = plr.Character.UpperTorso
end
end)