In this area of the US, crab crass is considered a stubborn, pesky weed. It is seen in cracks in patio stones and lawns.
Some people get quite upset about crab grass on their lawns.
There are a number of products that can be spread on a lawn to get rid of crab grass. These must be applied in very early spring.
The thing about crab grass is that it seeds itself. If there are bare spots in a lawn in autumn, the crab grass will settle its seeds in for the winter. The following spring, the crab grass grows quickly.
This type of crab grass is called Digitaira sangunalis.
There are other kinds of crab grass.
All the pictures are from Wikimedia Commons. Except for one.
These three pictures are of the Digitaria sangunalis. This is the crab grass that makes grown people cry. The first two are by, Matt Lavan from Bozeman Montana, USA.
These two pictures are of Digitaria ciliaris.