How would one stop a player from jumping?(Partially Solved)

Basically, I am making a script to stop a player from jumping if there 'stamina' is under 15. When I test it in-game, it shows no errors, but doesn't work, so here is the script.

--The script is under the screengui.
local sa=script.Parent.S--A int. value under the screengui.
local fill=script.Parent.Main.Fill--A frame to go over the main part to show visually where your stamina sits.
local hum=script.Parent.Parent.Parent.Character:FindFirstChild("Humanoid")
local txt=script.Parent.Main.TextLabel
coroutine.resume(coroutine.create(function()
while true do
    wait(3)
if sa.Value < 100 then
    sa.Value=sa.Value + 10
elseif sa.Value > 100 then
        sa.Value=100
    end
end
end))

coroutine.resume(coroutine.create(function()
while wait() do
    fill.Size=UDim2.new(sa.Value *0.01, 0, 1, 0)
txt.Text="Stamina:"..sa.Value.."/100"
end
end))

hum.Changed:connect(function()
    if sa.Value >= 15 then
        sa.Value = sa.Value -15
    else --Implying speed is a factor in this
        hum.Jump=false
    end
end)

Thanks in advance. :)