Annual or perennial sedge grass. If you had stalks on it.......I would consider kyllinga.
However, Certainty will get rid of it. Solitare and Celcius will do it also. They both are pricey!
Sedgehammer and these products containing halosulfuron will suppress it.
The problem with sedges is---this weed develops a fibrous under ground network of rhizomes that form nuts on the end of nodes. These are like bulbs that develop into a new plant. You can spend many hours pulling these things up but if you leave a stem in the ground.......it will resume growth. You have to get all the rhizomes and nutlets dead.
These weeds just love moist areas with thinning turf. Sometimes it grows in thick turf but prefers thinning spots. Compaction and poor drainage is the usual culprit.
You are going to spend somewhere around 100.00-200.00 for a container of the good stuff to do the trick. For me.....it is nothing as I need it to do the job and not piddle with the reappearances of stems.