In lawn with a reddish tint, weed?

Are you able to send us additional photos for ID? We cannot determine the species from these photos, unfortunately, as we cannot see enough detail or foliage characteristics. A picture of the plant growing as-is in the ground (from just enough of a distance that we can see it's growth pattern and size of the patch) as well as another close-up of uncut foliage, is possible. Regularly mown stems creates unusual growth patterns that can complicate identification features.

You can attach up to three photos to this reply, but you can reply more than once if you wish to send additional photos.

Miri

Here you go.

We think this is a combination of Japanese stiltgrass (an invasive annual grass) and nimblewill (a native perennial grass). Both are weeds and will go brown in the winter. Stiltgrass sometimes gets a fungus which turns patches of it brown, and yours may already be turning brown in preparation for winter.

They have very different management approaches.
https://extension.umd.edu/hgic/topics/japanese-stiltgrass
https://extension.umd.edu/search/node/nimblewill

You can aerate and overseed, or use a slitseeder to seed now--or rake/rough up the soil. At any rate, get good soil to seed contact. To overseed, you'll need to do so in the next couple of weeks. Here is how to renovate and overseed:

Ellen