What is wrong with my car if it spits and sputters when turned off after a long drive and is leaking a little water on the ground?

What is wrong with my car if it spits and sputters when turned off after a long drive and is leaking a little water on the ground?
This is because your vehicle's engine is almost at the highest operating temperature as you drove a long drive and you may have shut the engine down without letting it to cool for a minute or two. here what happens is your engine is hot and the heat is exchanged through the radiator to atmosphere when you stop the engine it does not do as it runs. the stored heat energy in the engine rises the temperature and boils coolant when you shut the engine off immediately after a long drive.
this habit is especially not good for some of the engine parts such as turbocharger, oil seals and rubber gaskets. I guess this is your case as i guess all other parts of your engine works perfectly.