Qinwen Zheng’s Rising Tide

Qinwen Zheng at the 2024 US Open

Since a first-round exit to Lulu Sun at Wimbledon this year, Qinwen Zheng has transformed herself from a rising prospect to a force at the top of the women’s game. The 22-year-old has won 30 of 35 matches, picking up three titles including an Olympic gold. In her first appearance at the tour finals this week, she has defeated two top-five players and earned a place in the semi-finals.

Zheng currently sits at 7th in the official rankings, equal to her career best. Her performance in Riyadh will move her up to at least sixth. Elo, a leading indicator as usual, already considers her the third-best player in the world, behind only Aryna Sabalenka and Iga Swiatek. The Chinese player is riding an astonishing 30-2 streak against everyone not named Sabalenka, so it’s hard to argue.

What has changed? Zheng has long been ticketed for big things. Her January run to the the Australian Open final indicated that she was reaching her potential. But she made only two quarter-finals in the next ten events, losing both. There were clear weaknesses in her game then. Has Qinwen 2.0 plugged those gaps?

Lifting all metrics

When I last wrote about Zheng, I referred to her serve as “under construction.” Her first serves were (and are) among the very best in the game. But she missed often, and her second serve was below average for a top-50 player.

I proposed an admittedly theoretical solution, that she could play somewhat more conservatively on the first serve, still winning plenty of points. Then she could go (relatively) bigger on seconds, trading a few more double faults for better results. The bottom line, at least according to the algorithm, was that the shift would increase her serve points won from a good 60.1% to a great 61.7%.

She hasn’t done any of that. Yet since leaving Wimbledon, she has won 63.3% of service points. That’s better than the full-season mark of anyone except Swiatek.

Qinwen found a blunter solution: She just got better at everything. Here’s an overview of her serve and return results for the two halves of 2024–up to and after Wimbledon–as well as her hard court results in 2023:

Time Span        W-L  1stIn%  1stW%  2ndW%    SPW    RPW  
2023 Hard      26-12   51.9%  74.3%  45.7%  60.5%  43.6%  
2024 1st half  19-12   51.5%  74.9%  45.5%  60.6%  42.9%  
2024 2nd half   30-5   53.8%  76.5%  47.9%  63.3%  45.9%

First serves in? Up two percentage points. First serves won? Two points. Second serves won? Two points. Return points won? Three points from the first half of 2024 to the second, even though the average surface is faster.

These are enormous shifts. 54% of first serves in still leaves her near the bottom of the table, but moving from 60.6% to 63.3% serve points won is the difference between the edge of the top ten and, as noted, number two. Key to the move is the rate of second serves won, which improved from the bottom third of tour players to the top half. On return, 42.9% to 45.9% is a jump from the bottom quartile of tour regulars to the top.

In short, Zheng went from having weaknesses to not having weaknesses. It’s never easy to divvy up the credit between player and coach, but if Pere Riba doesn’t win coach of the year, we might as well quit giving out the award.

Ratioing the tour

One of the goals of my research is to help us be more specific when we analyze players. Zheng’s various points-won rates give us a clearer view than just going goggle-eyed at a 30-5 record. But it’s tough to pinpoint a player’s improvement when she suddenly does everything better.

Qinwen’s rates of winners and unforced errors leave us in the same conundrum: She’s just gotten better by every conceivable metric. Still, I have to share. Sometimes it’s worth going goggle-eyed.

I have winner and unforced error stats for a limited subset of matches–77, in Zheng’s case–from a combination of grand slam data and the Match Charting Project. For the 58 matches through the loss at Wimbledon, she hit winners on 16.9% of points, versus UFEs on 19.2%. That works out to a ratio of 0.88, which is quite good. Commentators like to point to a 1:1 ratio as a goal, but that’s relatively rare on the women’s tour. 0.85 is usually sufficient to win a match.

Since July, the Chinese player’s W/UFE rates have basically flipped. In 18 matches worth of data, she’s hit winners on 19.3% of points, against a 17.0% unforced error rate. Those numbers are good for a ratio of 1.14. Here’s a complete list of the women who have posted better ratios this year:

1. Aryna Sabalenka

That’s it. With more complete data, it’s possible that Zheng would outscore Sabalenka, too. We have W/UFE for four of Qinwen’s five second-half losses, but only 14 of 30 wins. The sample is probably a bit biased against her.

The backhand complement

When I wrote about Zheng in January, her forehand–assessed by my Forehand Potency (FHP) metric–already ranked in the top ten among tour regulars. Her backhand remained a question mark.

If there are any specifics we can glean about the 22-year-old’s improvement, it is here. Until the beginning of this season, her backhand was, more or less, a neutral shot. The Backhand Potency (BHP) stat measures how often a shot ends the point for or against the player, as well as how often it sets up a point-ending shot shortly thereafter. In 2024, Qinwen’s backhand has been five times more effective that it was before:

Time Span  BHP/100  Negative Matches  
2021-23        1.2          13 of 32  
2024           6.3           6 of 34

In the past, the Zheng backhand cost her points–that is, it rated a negative BHP–nearly half the time, in 13 of 32 charted matches. This year, it has rarely done so. While BHP per 100 backhands (BHP/100) can’t be directly converted to a number of points per match, it’s safe to estimate that her backhand is now worth at least two or three points per match that she wasn’t winning before.

A few points per contest are enough to separate a good player from a great one. The backhand alone accounts for a big chunk of the gap between early Qinwen and the current unbeatable model.

We can even see the connection between BHP and return points won. This year, Zheng has gotten more returns in play: about one percentage point more, despite the fact that she has played Sabalenka so many times. Often, pros increase that metric by playing more conservatively. They send more balls back but do so weakly, losing most of those points. The Chinese woman, on the other hand, has also improved her win rate when she puts the return in play. That number–at least in the sample of charted matches–has risen from 53.8% to 56.8%.

Return stats aren’t all about the backhand, but when someone has as dangerous of a forehand as Zheng does, opponents make the return as much about the backhand as they can. No longer anything resembling a servebot, Qinwen threatens in more and more return games. Last year, she earned a break point in 43% of (charted) return games; this year, she is up to 49%.

Up and to the right

At the risk of repeating myself: Every trendline for the 22-year-old is headed in the right direction.

Zheng has never beaten Sabalenka, but after losing 6-1, 6-2 at the US Open, she pushed the Belarusian to three tough sets in Wuhan. She had lost five straight to Swiatek, then straight-setted her on the Parisian clay at the Olympics. Last fall, Qinwen salvaged just three games against Elena Rybakina in Beijing. This week she beat her. Zheng needed three sets to get past Jasmine Paolini last month; yesterday she allowed the Italian a measly 37 points.

The only player left in the Riyadh field that the Chinese woman hasn’t defeated is Coco Gauff. They’ve met just once, in Rome this season. Zheng won just 44% of points that day, landing an abysmal 41% of first serves. Should the pair meet to decide the season-ending championship, Gauff may still have enough of an edge to come out on top. But if we’ve learned anything from Qinwen’s four-month surge, it’s that she’s going to play a whole lot better this time.

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