Guess your definition of fielding throws me for a loop. 1st, the ball never entered fair territory. What exactly did the catcher field. I would think catching balls/strikes would not be fielding because it is not computed in fielding pct. nor as chances. So in your def of fielding don't think...
I will try....Batter is called out, runner on third called out on an attempt to steal home plate, runner on second, thinking that was the third out runs off the the field and is tagged the catcher. Thus, unassisted triple play.