Nice photos! When you see little brown ants fighting on a sidewalk it's nearly always Tetramorium immigrans. The pavement ant.
I'm tempted to say that's the only species here, but the photos aren't close enough to tell. They are doing the "mandible locking" move that these colonies tend to do when fighting each other.
There are some stills showing how they lock mandibles and hit each other with their antennae... they don't always kill each other...
futurebird