Question
Hey. My question is this; this morning I was hit on the head by a baseball-sized large light-green textured ball from a tree as I walked to work. I live in Virginia, but remember these large balls on trees in my home state of TN. As a kid, we used to cut them open and "milk" was inside. And sometimes we would throw them at each other. What are they and what type of tree? Thank you.

Answer
Sounds like Osage Orange.
The Osage-orange (Maclura pomifera) is a plant in the mulberry family Moraceae. It is also known as Osage-apple, mock orange, hedge-apple, horse-apple, hedge ball, bois d'arc, bodark (mainly in Oklahoma and Texas), bodart (in northwest Louisiana) and bow wood. Common slang terms for it include monkey brain, monkey ball, monkey orange, and brain fruit due to its brainlike appearance.

Fruit: Pale green globe, three to five inches in diameter, made up of numerous small drupes, crowded and grown together. These small drupes are oblong, compressed, rounded, often notched at apex, filled with milky juice.

Native to the rich bottom lands of Arkansas, Texas, and Oklahoma. It has been widely naturalized throughout the U.S. and Canada.

The wood of the Osage-orange is golden yellow or bright orange when first cut, but turns brown on exposure. The wood is extremely hard, heavy, tough, and durable. It also shrinks or swells very little compared to the wood of other trees. The wood is used for fence posts, insulator pins, treenails, furniture, and archery bows. In fact, many archers consider the wood of the Osage-orange to be the world's finest wood for bows. (The name bodark is from the French bois d'arc mean "bow wood.") Also, a bright yellow dye can be extracted from the wood.
It is the fruit of the Osage-orange that most individuals find intriguing. In the hands of a child, the fruit can become dangerous weapons.

Here is a web link to pictures of the fruit.
http://hedgeapple.com/hedgeapplepics.html