I'm thinking it's a Peltier Rainbow. There was a bubble just beneath the surface and the glass covering it shattered. That's why the bottom/sides of the hole is smooth and the upper/surface edges are rough. These are often referred to as "blowouts". A "bubble pop" would be smooth all around.
@Royal3 That's a nice Alley and it looks to be in excellent condition - the glass is so soft on those they're usually pretty beat up. Have you ever seen one in player size?