Here's the good news. It's a tennis ball. This isn't going to cause too much damage. If it were a baseball then we might have a problem, like the time my dad threw a baseball at my eyeball. OK, so maybe that's not fair to him. He through a totally valid throw at me and I failed to catch it. Well, not totally true. I caught it with my eye socket, but nobody is getting drafted into the MLB for their skill at catching with their eye socket.
I wonder what this person was doing throwing a ball at someone holding a camera. That's a jerk move. Hopefully that's a cheap camera. Don't ever throw a ball at someone with an expensive DSLR. That could end up being a $1,000 mistake. Lenses alone could cost over a grand.