rachelmickey's Identifications

This observation is a very active interaction /combat? mating? territorial defense?? taking place between two different sized pillbugs on the paved base of the HVAC condenser. This mundane piece of concrete became an arena for quite the meeting of the champions. The area is often damp on the surface, and in the shade. I observed this encounter While mowing, and watched for a couple of minutes as the larger pill bug moved around and raised up on its hind legs and the smaller pill bug held on and repositioned itself several times. During the several minutes that I watched, it never ended. What is going on here? Are these two the same species or different species, I do notice a color difference, as well as the size difference.