Where do you live? Would you characterize the dark green area as either higher or lower than the surrounding grass? Does water accumulate there? When were the last two times you fertilized and what did you use? How high/low do you mow and how often? What is your watering regimen? How often and how long each time?

Chances are they are goners. Tug on the stumps and see if they feel like they are strongly rooted. I'm going through this now with several grasses, including some which may be hardy in my zone and some which certainly are hardy here. I installed three Arundo 'Peppermint Stick" plants last fall, after growing them on in 15 gallon pots through the summer. One started re-growth in mid-April, and another just started this week. The third is still silent. I planted 3 each Pennisetum 'Prince' and 'Princess' last summer, and all 6 grew with abandon. They were gorgeous. So far, none have re-grown. We had a zone 8 winter, so I had high hopes. It doesn't look good.

crab grass, an annual weed grass. Your options are to 1) spot-spray it with Round-Up, although you will also kill surrounding grass with overspray, 2) hand-pull it 3) combo hand-pull/seedhead control this year and application of a pre-emergent NEXT year. If it were my yard I would hand-pull the crab grass and immediately treat bare spots with turf seed to fill back in.

+1 Julian. Anything from dog urine to deer urine to the beginnings of a really severe fairy ring are possible.