Here is another picture. Thanks for any help you can provide.

Looks like crabgrass. You can use a crabgrass killer. Next spring put down pre-emergent when the forsythia bloom.

Plus the grass looks thin enough (common for sandy Maryland soils) to allow for plenty of crabgrass growth. Feed well this fall to fill it in, and consider using an organic to increase the soil health. Milorganite from your local big box store is fine, or grains if you can get them.

(For Maryland soils, a soil test from Logan Labs or UMass is a very good idea as well, they're typically resource short, which is limiting the grass and allowing the crabgrass to grow more easily, but this is optional).

The crabgrass will die in the fall after frost. So you don't have to kill it now. Herbicides will stress your grass somewhat and summer puts the lawn under stress anyway. So you have to decide whether the herbicide or the growth of the crabgrass is more stressful to your good grass. If you use an herbicide (like Weed B Gon with Crabgrass Killer), read and follow directions. I haven't used it (I've had success with pre-emergents). Some herbicides require that the air temperature be under a certain level.

Would you characterize your lawn as thin-ish? Usually crabgrass and other weeds sneak in via the bare soil exposed to the sunlight. I know Mother Nature has decided this year to flood lots of yards, and that helps germinate weed seeds. What kind of grass do you have?