Might be Japanese stiltgrass, Microstegium vimineum.

https://gobotany.newenglandwild.org/species/microstegium/vimineum/

That was my thought as well :-) Knowing your location would help......stiltgrass is a very common invasive species in the eastern US.

It does make a decent looking groundcover look-alike, however its bad behavior and drawbacks greatly outweigh its pleasing visual appearance.

It can likely be controlled now by weed whacking it to the ground before it sets seed. I just did that at a vacant lot on my street. Since it's an annual grass, the number of seedlings will be greatly reduced next year. I would like a closer view to be certain but don't know of anything else that looks like it.

I am in central New Jersey. This comes back every year in the same place. I have always admired it. But if it is a weed will change my tune. I will get a closer pic tomorrow.

Yep, Japanese Stiltgrass, a terrible and dangerous invasive that threatens woodland biomes...but unlikely to be controlled at this point, especially since for 1/2 the hayseeds (no pun intended) in my neighborhood, this is what their main shade species of grass is! And crabgrass is their sun species lol.

You can try to cut it before it sets seed, but it is sometimes tricky to get every last one. It will try to regrow and quickly set some seeds. And you can be sure there will be some hidden away you won't see in time. Luckily it is fairly easy to pull as weeds go.

In a fescue lawn, Acclaim can control it but needs about 2 weeks to kill it. Acclaim can also be used over the top on most ornamentals. It has a sneaky way of clambering through azaleas for example...I would pull it if there was just one, but back when there were hundreds, it was easier to spray! But that's a "professional" product and probably beyond some people's mental facilities to apply correctly, so not something I'd officially recommend.

I had about 1/2 acre completely overtaken by it - the prior owners had had it as their shade grass species, too - that I got under control with Surflan, Acclaim and Gyphosate.