I think that is bentgrass. There are at least two species that come into question. One is creeping bentgrass with stolons and long ligule and the other is colonial bent with rhizomes and short ligule. The ligule seems to be relatively short, so I suspect colonial bent (Agrostis capillaris).

 

Dig out I suppose? luckily it's only a 2' diameter. I don't see it anywhere else.

 

If it's the one with rhizomes, make sure to catch them all, or paint with glyphosate. That's what I did.