I was talking about this in another thread, but I had not put all the numbers together carefully. I was calling aces free points, and thinking of DFs as giving away free points to the opponent. Several people objected to this as a valuable metric, saying that DFs are also tactical (when is it wise to go for the 2nd serve), and that not counting unreturnable serves and weak returns is too simplistic. My points: From aces, we should also get an idea of the relationship between them and unreturnable serves, and weak returns. This should be, roughly, somewhat predictable. Aces and DFs are recorded well, at least since 1991, so it's something we can look at for all players. Good luck getting data for unretunables and weak returns. But for the moment, I'm going to ask people to go along with what I'm doing, to see where it gets us. One statistic we can instantly track is this: How many DFs per game? Because this tends to show how "clean" the service game is. No one likes to give a way points. I tried to include in my list of players all players who are known for having very effective serves. Not the most aces, but the guys who top the % of service games won. This list includes the guys who are servebots, the guys who smoke the ball and get a ton of free points, but it also includes players who have a relatively low ace count but who win a lot of games. One of the first players I checked was Dolgopolov because of his quick release serve and reputation for being a very good server, for someone his size. But it turns out that he fails as a very good server for two reasons: 1. Only .35 aces per game, meaning he has to play about 3 service games to ace once. This by itself is not bad at all, for a shorter guy. He also aces nearly three times for every DF, which is not bad at all, but when you subtract DFs from aces, the net is 1 clean free point every 4 games. This is about the same as Djokovic, so again, not bad at all. But still fairly far down on the list. 2. Of all the guys I checked, his % of service games is second worst, with only Chang down a bit more. Neither won 80% of their games, career. But numbers were lower, across the board, in the 90s. No poly. So Chang was no doubt more effective in winning service games, and very close to the Dog in aces per game. The second lowest guy in my list, DFs to games, is one of the best players in tennis, in this era. Question: Who do you think that player is? You may find someone else even better, career, all surfaces, but I'll be shocked if it is anyone who any of us think of as a great player. Guesses?