Japanese stiltgrass. An invasive annual that takes over. Left alone it grows about 2 feet. It flowers at end of summer. Easy to pull. Don't let it go to seed. It will flower and seed at ground level when mowed. It has carpeted the forest floor and roadsides here in NY, pushing out all other plants.

haven't cut the grass in 2 weeks...still the same 2 inch height..also some or all are very hard to pull....

Mine looks just like yours even with no mowing for weeks and with sprinkler watering of nearby garden. They're hard to pull when clustered and mowed like that.

I just pull what gets into my garden. I don't have the energy to get rid of it all or the desire to poison the planet. It's out of my hands.

I just looked up "nimblewill" and it does look like that. But that plant is a perennial, coming back every year. Maybe that's what it is. Have to look at it further. It's new to me.