No, not baseball (although this was the name of my graduate school softball team). And not a reference to non-existent fly scrotums, either.
They sometimes go by the common name of “snipe flies”. The behavior of this Genus is nicely summarized in the journal Psyche.
The adults do something very odd–the females cluster together in this ball when they lay eggs. They usually do this over water–so that when the eggs hatch, they drop down in to the water.
It could be an adaptation to group larval emergence in time and space. While some maggots will be eaten, the sheer numbers appearing at a short interval in time makes sure that a few will be missed. A giant clump of dead flies also will serve to discourage a lot of predators, so the eggs in the center should hatch safely.