I would have called it an unforced error. Yes, Djoker had him moving. But Fed went for the line and missed. He didn't need to, he could have played it elsewhere. But he went for the line and missed. To me, if a player goes for a winner and hits it out it should be an unforced error. (Is this assumption incorrect?) Also, although he was moving to the ball his footwork was not what we would see on a very wide ball that he could barely get to. Technically, it was not hit "on the run." Just after hitting that shot he was already back on balance and would have recovered position, ready if Djokovic managed to return the down the line shot. Also, I would call this a fatigue error. I can't find the reference right now, but accuracy is severely impacted due to motor control impairment once a person gets winded. I think Fed was getting fatigued, got a good look at the line and had the choice of staying in the rally and doing some more running or taking a shot at the line. He took it and missed. Unforced error in my book, as a result of fatigue, with deference to the experts. On the other hand, if the fatigue error hypothesis is correct, one could say that Djokovic made him run in the rally, fatiguing him, and thereby forced the error. But Djokovic was also being made to run, but didn't miss. In my opinion this is one of the reasons Djokovic would prefer to get Fed into long rallies and why Fed would have liked to pull the trigger prior to this. Haha. Then, to the contrary, one could say that Djoker forced the error by pulling Fed into a long rally where he knew his own fatique would handicap his style less than it would handicap Federer's. (This may be an example of that player bias we were talking about before. I've seen Fed make that shot before, and miss it before. I expect him to make it off the ball Djokovic gave him in this instance. Maybe that expectation is unrealistic. Maybe this would be a shot where Federer would say, "Man, you don't understand how difficult that is! Yeah, I make it sometimes, but that's because I'm Federer!") Anyway, my two cents. I'll consider any responses as part of my eduction as a novice box score man. I had no idea errors were this complicated.