If the sump is cracked, there would likely be 4 litres of oil on the floor which would be a hell of a mess.. covering a driveway and more. If it's less than that, you mgiht have a failed rocker cover seal or something.
Look in the engine – if there's oil coming out of the top of the engine, then that could be it. Rocker cover would only leak when the engine is running tho.
If the car is sat for more than say half an hour and it's still dripping, then it's the sump, really. Because all the oil sits down there underneath the engine when it's off. Oil leaking from elsewhere in the engine will only happen when it's running… but as you have an undertray, that can collect oil and release it when you park on a slope, say.
Check the rest of the engine for oily streaks I'd say.
Oh, and to crack the sump you'd have to smack it hard on the ground somewhere, I think you'd remember this happening if you did it and be able to easily relate it to the leak 🙂