Seems to me like a few factors played into this: The ground was slippery, and the rider was asking the horse to move quickly in a circle on slippery ground. Scary yes, but pretty preventable by riding on turf that is not slick, or doing appropriate activities on slick turf. Glad they're both ok.
JustDressageIt- Yeah, What we figured was the top was completely dry (cause it was dusty and dry) but underneath it was wet (found that out afterwards) it looked to us that it was totally dry, his feet didn't even leave foot prints. I had no idea it was wet underneath so we were working circles after doing a lot of warm ups...I was working circles to get him ready for the turns we'll have to do for gaming. I really wish we had a proper riding arena but I'm just happy Phantom's being taken care of here. =D
We're both fine checked Phantom's legs when I put him in the stall tonight they were fine I'm going out and checking tomorrow morning to be totally sure.