Can you identify this weed?
This looks like Japanese stiltgrass. Here is some information.
Next spring apply a preemergent to control stiltgrass.
Apply prior to seed germination which begins, in early spring a couple of weeks before crabgrass seeds germinate. Seedlings emerge about the same time as crabgrass. Look for the active ingredient: Prodiamine (Barricade) or other preemergents labeled for crabgrass control. Keep the area mowed to help prevent the stiltgrass from forming seeds.
For post emergent controls look at the publication from Rutgers. Fenoxaprop (trade name Acclaim Extra and Bayer Crabgrass Killer for Lawns) is listed. We do not have research on their effectiveness. This is not labeled for professionals.
Stiltgrass likes shade and will move into bare spots. The best defense is a thick stand of turf. https://extension.umd.edu/hgic/problems/japanese-stiltgrass