Another angle on projecting young players: How good will Alcaraz, Sinner, etc become?

[El Dude]

One of my fascinations with tennis analysis is thinking about how good any given young player will eventually become, and whether there is any way to assess this through looking at their statistical record. In the past, I came up with a list of "benchmarks of greatness" - statistical accomplishments that every all-time great (defined as 6+ Slam winners) accomplished at certain ages, such as reaching certain ranking thresholds, first big title, etc.

What follows is another angle based on Elo. I looked at the Elo rating of different players on their birthdays, from age 18 to 29, spanning the developmental period (18-21) and the typical prime years (21-27) and possibly first signs of decline (late 20s).

First off, here's the Big Four as well as a handful of very good to semi-elite players of recent decades:

The chart might be a bit confusing (and note that the numbers aren't always exactly aligned with the first column, due to how close some are ranked), but let me unpack it a bit. First off, the second black column is the average Elo rating of different ranks (by year-end Elo), which gives us a rough sense of how good each player was at a given age, relative to historic norms.

I've included the Big Four in darker colors, as well as a range of very good to semi-elite players: Gasquet, Dimitrov, Nishikori, Cilic, Berdych, and Del Potro.

Note that Rafael Nadal is an outlier - at least early on, until age 21-22 when others catch up. Meaning, he shouldn't be considered as a marker against which young players should be mentioned, as far as his age 18-20 performance, considering that the similarly accomplished Roger Federer and Novak Djokovic were slower to develop (especially Federer).

A few things can be gleaned from the above:

One, look how closely grouped everyone is at age 19. Every player had enough time to warrant an Elo rating, and almost everyone is very close - with only Rafa far ahead. The separation begins to occur after players turn 19.

By age 20, you have the greats above the lesser players. Meaning, the separation mentioned above occurs between age 19-20...in every case. There is still variation in development, but something happens between age 19 and 20...as if it is a crucial early part of their developmental arc that determines future greatness.

It is also interesting to note that Del Potro, at age 20, is grouped right there with the greats, just an inconsequential 10 Elo points behind Federer and a far more substantial 71 points ahead of the best of the second grouping, Cilic.

Two, almost every player plateaus at age 20-21 or 21-22, with only minor variation. Rafa plateaued at 20-22 before jumping up at 23 (which he turned in 2008, when his level rose and he won his first non-clay Slam). Novak plateaued at 21-23 before jumping in 2011, when he was 23-24. Murray and Federer plateaued at 20-21 before jumping up after, by their 22nd birthday.

But here we also see the separation. Whereas the Big Four all plateaued for 2+ years somewhere in the 20-23 range before jumping to a higher level, all of the lesser players didn't have that jump. Most took a more gradual route of improvement. Dimitrov improved every year up to his 24th birthday, then fell back by his 25th birthday, then rose back again, with his highest "birthday rank" being age 27 (in 2018 after winning his two big titles the previous year).

Even Andy Murray, who I used to call "the worst of the best and the best of the rest" was right there with the other Big Four on his 22nd birthday, but then plateaued and didn't have that big jump to GOAT level until after he turned age 29 in 2016, so off the chart.

Del Potro is another outlier. Up through age 21-22 he looked like he was on the path to greatness, but then injury struck and he never returned to that level, though still performed at a high level.

Meaning, just as we see one separation at age 19-20, another occurs after that age 20-23 plateau, in which the Bigger Three made another developmental jump to truly stellar levels, beyond even that of previous all-time greats (e.g. Agassi, Sampras, Becker, Edberg and Wilander all peaked in terms of Elo in the 2370-2420 range; you have to go back to Lendl, McEnroe, Borg, and Connors to find 2500+ Elo players).

Three, note that Novak did something that neither Roger nor Rafa did: After peaking in the mid-20s, Novak actually continued to go up in his late 20s when Rafa and Roger were settling in at a lower post-peak level.

Finally, note that some of the lesser players had jumps later on in their careers: Nishikori at age 25, Cilic at age 26, Berdych at age 27. Not huge jumps, but still finding a higher level in the second half of their 20s. On the other hand, poor Gasquet had the second highest age 19 Elo other than Rafa, but then stalled and while he gradually improved through most of his 20s, never had that big jump from being a merely very good player to a great one.

Part 2 is upcoming, in which I look at the current young players.

 

[El Dude]

Alright, to continue.

To summarize the key points from Part 1, we determined that:

1. Talented players are closely grouped -- that is, similar in Elo rating -- around age 19, and begin to separate after their 19th birthdays. By age 20, there is a clearer distribution of the greats above most everyone else.
2. Most players go through a plateau of at least a couple years somewhere in the age 20-23 range, after which the true greats end up jumping even higher and the lesser players develop more slowly.

In other words, we see one separation of greats and everyone else between age 19-20, and then a further separation sometime between age 20-23; by age 23, it is generally very clear who will become an all-time great.

There are outliers. For instance, Andre Agassi reached an up-to-that-point peak Elo of 2246 at age 20, then plateaued (or stagnated) for several years, before jumping again at age 24-25, when he had one of his very best seasons in 1995. This is a good reminder that these names aren't just statistical concepts but real people: Agassi was a young player known for his antics, on and off the field. For those who remember Agassi in the early 90s, it is probably no surprise that he saw no real development in his game in his early 20s.

To go further, if you look at the peak Elo ratings for every all-time great (6+ Slam winners plus Murray) up to certain ages, you have some minimum thresholds:

age 20: 2017 Elo
age 21: 2150 Elo
age 22: 2231 Elo
age 23-24: 2246 Elo
age 25: 2364 Elo
age 26+: 2370 Elo

Meaning, no all-time great had a lower peak Elo rating than the above at the age listed. Lesser greats (e.g. 2-4 Slam winners) and second tier types (0-1 Slams, regulars in the top 10) vary more widely, to the point that there's no clear developmental thresholds. For instance, Daniil Medvedev barely surpassed 1800 Elo by age 21 as he started late, but has reached a higher Elo rating than many players who blossomed much younger.

The point being, the above thresholds give us indicators for true all-time greats, but not anyone else.

How do our current crop of Next Gen and Millenials players fare, compared to the above? Well, here is the age of current players and their peak Elos thus far. Green means they're above their relevant threshold, black below:

Age 27: Medvedev 2316, Norrie 2105
Age 26: Berrettini 2173, Khachanov 2137, Coric 2102, Hurkacz 2099, Garin 2010
Age 25: Zverev 2303, Rublev 2227, Fritz 2123, Tiafoe 2061
Age 24: Tsitsipas 2258, Ruud 2163, De Minaur 2083
Age 23: Shapovalov 2075, Fokina 1998
Age 22: Auger-Aliassime 2140, Korda 2071
Age 21: Sinner 2175, Musetti 1988, Lehecka 1916
Age 20: Alcaraz 2238, Rune 2089 (both turn 20 within the next month)

What we see above is that there are only four young players who have reached their relevant Elo thresholds at age 20 or higher so far: Alcaraz, Rune, Sinner, and Tsitsipas.

Alcaraz has already "graduated" to age 22; Rune is fine for his age 20 Elo threshold, but needs to keep on developing to 2150 by April of 2024; Sinner needs to jump a bit more to 2231 from 2175 by August to reach his next one. Tsitsipas--who has stagnated for a few years in terms of Elo--needs to take a big jump this year, before December, to reach that 2364 Elo threshold (In truth, 2350 or so is what separates the true greats from everyone else, and every all-time great had reached it by their 25th birthday).

In fact, with Tsitsipas we see a similar developmental arc to Andre Agassi, who reached 2246 Elo before his 21st birthday and then didn't rise again until after turning 24. Tsitsipas reached 2175 Elo at age 21 (similar to Sinner), then peaked at 2258 at age 22 and hasn't gone higher since, in almost two years. Tsitsipas is about the age Agassi was when he started his age 24-26 peak.

(Andre's in blue, Tsitsipas in red)

As you can see, Andre started much younger--as did most players during that era--but by age 21, Stefanos was right there with them. The chart clearly shows that Andre made a big leap at around Stefanos's current age (in fact, the young Greek is a hair behind so needs to get going).

Or to put that another way, Alcaraz is the only one who seems clearly on the path to greatness. It isn't a sure thing, as he still needs to make that next developmental jump from "pretty great" (<2300 Elo) to "truly great" (2350+ Elo), but he's got plenty of time to get there. Note that he's not quite as early blooming as some all-time greats--Wilander (2368), Nadal (2360), Becker (2359), and Borg (2328) had all surpassed 2300 Elo by their 20th birthdays (though technically Alcaraz still has a chance, with Barcelona, Monte-Carlo, and Madrid all before his 20th birthday on May 5). But he's right there with Edberg (2243 at age 20), and ahead of all the other ATGs.

Rune has the potential, and his peak of 2089 before age 20 is higher than that of Jimmy Connors (2068) and Ivan Lendl (2017) and just below Roger Federer (2110). But he's also young enough that it is hard to make a hard determination; we'll know more in the next year or so, and one key will be reaching the 2200 threshold sometime before his 22nd birthday...but that's not until 2025.

Both Sinner and Tsitsipas are on the cusp and need to make big jumps this year, especially Tsitsipas. Sinner is actually on a similar Elo trajectory to Federer, who among all-time greats was a slow bloomer. Sinner's peak Elo is 2175; Roger's peak was 2168 when he turned 21, and 2231 when he turned 22, then he had a big jump after to 2388 by age 23 and 2470 by age 24. Meaning, Roger made a huge rise after his 22nd birthday to stratospheric levels by age 24.

Compare Federer (red) and Sinner (blue):

Now perhaps comparing Sinner to Federer isn't fair to the young Italian, but the similarity is quite striking. Aside from a down-turn before his 21st birthday (August of 2002), Roger's rise was steady and, as his peers knew at the time, inexorable. It will be hard for Jannik to continue rising like Roger did, but you never know.