The prey is definitely a lycosid of some sort.

I noticed that the spider is missing a leg. I was wondering if this photograph was the exact moment you saw it or did you have a chance to observe it for a few moments? A few species of Anoplius have been known to chew at body parts or sever legs and drink the exuding haemolymph (i.e. A. relativus, which this wasp very closely resembles).

I made an error in putting Episyron. I have 2 of those with the stripes, and I meant Anoplius, so I agree.

I found the spider on the rock. I noticed that it was not dried up dead, and surmised that it was might be paralyzed. I set up and waited as I saw an Anoplius wandering around. Several times it came within a couple of inches of the spider but never touched. Then it started digging in the bank of the stream where this occurred. It just kept digging and I was in a very uncomfortable position on the edge of the bank. While that wasp was digging another Anoplius came along and approached the spider and I shot it, but I gave up as it wandered away also, and I felt I'd spent enough time. If I hadn't had a whole series of one dragging a spider a few weeks before, I might have been more patient, but about 45 minutes in this cramped waiting position was enough that day, and I continued shooting other things.