Fresh Water Lobsters?

Of course the pet store bills them as lobsters and sticks them with price
tag to match, but I believe they're Crayfish. Here is the question.

I have two of these. They came from the same store, same tank, same time.
They live in a 150 gal. fresh water tank with a 2'x4' natural gravel floor,
plenty of slate shelves, cave, and hiding places and food. I mean, we're
talking luxury condo with plenty of room for everybody right?

Wrong!

One of these two is always traveling in reverse, being pursued by the other.
The larger is always running from the smaller. For months I never saw them
catch up with each other. But this week the smaller one is catching the
other one all the time in a very violent wrestling display.

Once caught, the aggressor tangles the other in a sleeper hold that
professional wrestlers would envy, and keeps it there until... well...
I've taken them apart several times.

Ok, here is the question. Am I doing the right thing? Is one exhausted
from running? Is it getting weak? Is it dieing? is one trying to kill the
other? OR is there just a little "som'n som'n" go'n on?

Let me know.

T