Its a puffball fungus - at some point, a hole will open up in the centre and spores will be spurted out of it. In fact, it looks as though a small central hole has already opened up in the largest one in your picture. This dispersal of spores sometimes occurs spontaneously after the fungus has been prodded or touched. As to precisely which puffball it is, there are several that look fairly similar, and mycology expertise coupled with a magnifying glass are needed to confirm the exact ID, but it looks like Vascellum curtisii, see link below
Grass is one of its favourite habitats, and it may occur as a single cluster like yours, or spread around and about.