I had about 8-9 oak root balls like that in my friends woods. They weren't quite as tall but had more dirt on it. I read a couple stories of kids getting crushed by playing in those holes when the root ball falls back when the stump is cut. I cut them off when I knew nobody was around and it dropped with a big thud force was incredible.
I never saw one fall back towards the direction of the tree and probably was careless in that regard. I should have had the FEL against it to keep from falling toward the tree.