Italian translation at settesei.it
Bianca Andreescu is really good, right now. Still a few months away from her 19th birthday, she has collected her first Premier Mandatory title, beaten a few top-ten players (including Angelique Kerber twice), and climbed to 7th in the Elo ratings. She is the only teenager in the WTA top 30 and one of only five in the top 100.
The burning question about Andreescu isn’t how good she is, it’s how good she could become. It’s easy to look at the best 18-year-old in the game and imagine her becoming the best 19-year-old, best 20-year-old, and so on, until she’s at her peak age and she’s the best player in the world, period. As the sport in general has gotten older, teenage champions have become rarer, so she seems all the more destined for success. But it isn’t that simple: Prospects get injured, opponents learn how to beat them, they peak early and fizzle out. Tennis history is littered with teen starlets who failed to reach their potential.
Building an aging curve
Let’s start with the basics. What is the trajectory of the typical WTA career? Answering that question requires a whole slew of assumptions, so keep in mind that this is approximate. I found every player born between 1960 and 1989* who played at least five full** seasons, a total of about 500 players. For each one, I calculated her year-end Elo for every full season she played, as well as the difference between that year’s Elo and her peak year-end Elo.
* I wish we knew more about players born in the 1990s, since their experience is most relevant to today’s teens, but many of them have yet to reach their peaks, whenever that will be.
** I’ve defined a full season very broadly, as 20 or more completed matches at the ITF $50K level or higher.
For every player, then, we have an idea of how they aged. To get our bearings, let’s look at a couple of players with unique aging trajectories: Martina Navratilova and Venus Williams:
(Martina’s peak was about 50 Elo points higher than Venus’s, but I set them equal to each other for the purpose of this graph.)
Venus peaked at age 21 and had her last all-time-great-level season at 23, while Martina’s peak came at age 30. There’s more than one way to amass a Hall of Fame career, and it’s important to keep in mind that “average” aging patterns hide a lot of more extreme possibilities.
The usual route
When we take Venus’s and Martina’s trajectories and average them with the other 500-or-so players in our dataset, here’s what we get:
The most common peak age is 24, with 23 a very close second. In the above graph, I set peak Elo at 1,820, the average peak Elo of the players I looked at, but the absolute number isn’t important. The typical player who completes a full season at age 18 is about 70 Elo points away from her peak. There’s isn’t much downward movement in the 20s; at age 30, those players who are still active are only 43 Elo points below their peak.
There’s a poison pill in that last sentence that is difficult to avoid when analyzing aging patterns–we only know what happens to those players who are still active. That’s even more troublesome for young players. Venus, for instance, improved 211 Elo points between her year-end finish as an 18-year-old and her best year-end rating. Kerber, on the other hand, wasn’t even good enough to show up in the ratings until she was 19. If we were able to estimate Kerber’s level at that age, it would probably be very low. Thus, forecasting an 18-year-old using this dataset may understate the degree to which a player can improve.
Changing times
Using the numbers above, we can make a baseline estimate. Those players who had year-end Elo ratings as 18-year-olds typically improved about 70 more points before hitting their peak. Through her Indian Wells title, Andreescu is rated at 2,017, giving us an estimated peak of 2,087. That’s good enough for 2nd place on the current list and just inside the top 50 of all time (as measured by the player’s best year-end Elo). Still, that seems a bit modest–it doesn’t represent much of an additional improvement for a player who has come so far in just a few months.
The forecast is slightly more optimistic if we narrow our view to players born in the 1980s. It seems like a reasonable thing to do, because Andreescu is facing an era with older competition, more like the last decade than, say, the one faced by players born in the 1960s. Our dataset shrinks to about 200 players, and those players do show a bigger gap between their 18-year-old Elo rating and their career peak. The difference is about 83 points, giving Bianca a revised estimated peak of 2,100–exactly even with Simona Halep, who currently tops the list, and around the 40th best of all time.
The biggest difference in the overall aging curve and the curve for players born in the 1980s isn’t the timing of the peak, it’s the duration. I looked at several age cohorts, and the typical WTA peak is always at 23 or 24 years old. But there’s more to it than that. Take a look at the trajectory of players born in the 1960s compared to those born in the 1980s:
For the more recent generation of players, there is little difference between age 23 and 28 or 29. Even into the early 30s, those players who stick around are competing almost as well as they did at their peak.
Bespoke for Bianca
Aging patterns in women’s tennis have changed, so it’s important to look at a relevant era when there’s enough data to do so. But what if that’s not the best way to narrow our view? As I’ve noted, the average peak Elo of the 500 players in our dataset is 1820. Bianca is already 200 points higher than that. What if the best players are qualitatively different as well as quantitatively superior?
Here are 20 players whose year-end Elo at age 18 were similar to Andreescu’s current rating: the ten closest who were higher and the ten closest who were lower:
Player Birth Year 18yo Elo Peak Elo Jelena Dokic 1983 2110 2110 Conchita Martinez 1972 2085 2191 Arantxa Sanchez Vicario 1971 2084 2314 Hana Mandlikova 1962 2071 2160 Iva Majoli 1977 2067 2067 Belinda Bencic 1997 2066 2066 Caroline Wozniacki 1990 2059 2194 Lindsay Davenport 1976 2053 2353 Nicole Vaidisova 1989 2043 2121 Manuela Maleeva Fragniere 1967 2035 2059 --- Mary Pierce 1975 2008 2161 Ana Ivanovic 1987 1994 2133 Victoria Azarenka 1989 1986 2270 Anke Huber 1974 1980 2072 Magdalena Maleeva 1975 1961 2024 Agnieszka Radwanska 1989 1957 2116 Mary Joe Fernandez 1971 1955 2110 Anna Kournikova 1981 1954 2020 Kathy Rinaldi Stunkel 1967 1947 1947 Justine Henin 1982 1946 2411
Both halves of the list include some of the greatest of all time: Arantxa Sanchez Vicario, Lindsay Davenport, Victoria Azarenka, and Justine Henin. Yet several of these players failed to build on their early-career peaks, such as Jelena Dokic and (so far, at least) Belinda Bencic.
The average 18-year-old year-end Elo of these 20 players is 2,018, virtually the same as Andreescu’s post-Indian Wells level. The average peak year-end Elo of these 20 players is 2,145, a 120 point improvement and a more optimistic forecast than anything we’ve seen so far. That rating would put her a tick above Ana Ivanovic at her best, a bit below Hana Mandlikova at hers, and just inside the 30 greatest of all time.
This is heady stuff for a teenager, but after watching her ascent this year, it’s tough to bet against her. And as long as Kerber is in the draw, apparently, we can expect Andreescu to keep winning.