This will make the player fall off vehicle, but u can do whatever you want below the "triggerServerEvent("onPlayerCollideVehicle", root, vehicle)", like make him lose his hp, etc.
function checkPlayerCollideVehicle()
local vehicle = getPedContactElement(localPlayer)
if vehicle and getElementType(vehicle) == "vehicle" then
triggerServerEvent("onPlayerCollideVehicle", root, vehicle)
jump_backwards()
end
end
addEventHandler("onClientRender", root, checkPlayerCollideVehicle)
function jump_backwards()
local x, y, z = getElementPosition( getLocalPlayer( ) )
setElementPosition( getLocalPlayer( ), x, y, z + 1 )
setElementPosition( getLocalPlayer( ), x - 2, y, z )
end