Does anyone know what this is?

During our trip to Basilicata we saw this "fruit" in a tree and all around it on the ground. I asked a very old man what is was and did not fully understand his answer but do know he said not to eat it. So, what is it and why grow it if you can't eat it?

According to Ginger: "It's called an Osage orange(Maclura pomifera)actually native to the US. Not edible. they were used for a thorny hedge plants between fields because they are hard to kill and withstand just about anything M.Nature wants to dish out."
Thank you Ginger