The receiver stud is partially staked in place.
It can be removed with a socket set, which supports things better than a single wrench, but its kind of scary since it feels like its going to strip.
Another trick is to use TWO wrenches, one on each side so its in a "tee" handle-like arrangement. This prevents binding.
Unless you absolutely have no choice, leave it in place.
To remove, back it out slightly, put some lube on the threads, then back in, then out a little more. Keep adding a little lube as it comes out and keep backing it in and out.
This will help "iron out" the staking and help prevent stripping the receiver.