Where tennis stats come from and when to trust them

Trace the stat to its source. Then trust it, or don't.

Key facts

1
About 70% of men's points and 66% of women's points end within four shots, in a secondary write-up of Craig O'Shannessy's charting.
2
Jeff Sackmann's Match Charting Project started in late 2013 and has more than 100 volunteers charting matches shot by shot, under a CC BY-NC-SA licence.
Jeff Sackmann, Match Charting Project
3
Hawk-Eye triangulates the ball's flight from several cameras, and the same trajectory yields speed, spin, bounce and placement. Its challenge system arrived in tennis in 2006.
Hawk-Eye Innovations
4
Craig O'Shannessy took his first-four-shots analysis to Team Djokovic from 2017 to 2019, a stretch that included four majors.
5
Strings return about 95% of the energy stored in them, while the ball loses about 45%.
Brody, Cross & Lindsey (2002)
6
A served ball lands at roughly 75% of the speed it leaves the racquet, so the radar number isn't what the returner faces.

Why it works

Tennis data was locked, messy and fragmented until people outside the tours built it layer by layer. Measurement came first: Hawk-Eye, built by Paul Hawkins, triangulates the ball from several cameras, and nearly every modern tennis number starts from that trajectory.

Then came rigour and open data. Stephanie Kovalchik publishes peer-reviewed rating and win-probability models and built tracking-data metrics at Tennis Australia's Game Insight Group. Jeff Sackmann's repositories and the Match Charting Project filled the gap the tours left.

Then coaching and biomechanics. O'Shannessy charted thousands of matches and showed that most points are short, which changed how players practise. Bruce Elliott's work on lumbar stress in adolescent servers changed how young players' load is managed. Segment work by Elliott, Marshall and Noffal shows the serve chain building from about 10 rad/s with the wrist alone to about 80 rad/s at the racquet tip with the full chain.

Every stat needs a camera, a denominator and a person. "Five points in a row, that's momentum" is a tiny sample. "70% of points end within four shots" stands, once you say which tour, surface and era.

The line to say on court
“Every stat has a camera, a denominator and a person. Find all three.”

Drill: The three-stat trace

20 min · alone

Watch one broadcast match and write down three on-screen stats as they appear.
For each, name the instrument (tracking cameras, a hand chart or a count) and the denominator (points, serves or matches, and which ones).
Name the person or institution whose work made the stat possible, and find one source page for it.

Number to beat3 of 3 stats traced to instrument, denominator and source

More drills like this: watch like an analyst

Faults and fixes

Believing the tours provide all the data

Independent tennis analytics exists because Sackmann freed the data.

FixCheck the licence line on any dataset.

Thinking Hawk-Eye just calls lines

It's the raw material for nearly every modern tennis number.

FixTrace the broadcast graphic back to the trajectory.

Quoting a rate without the sample size

Single-match samples are tiny and context dominates.

FixAsk for the denominator before the percentage.

Questions players ask

What percentage of tennis points end within four shots?

About 70% of men's points and 66% of women's, from Craig O'Shannessy's charting. It's a secondary write-up rather than a peer-reviewed table, so quote it with its tour, surface and era.

What is the Match Charting Project?

A volunteer project started by Jeff Sackmann in late 2013 that charts matches shot by shot. More than 100 volunteers contribute, and the data is licensed CC BY-NC-SA.

Is the serve speed on TV the speed the returner faces?

No. The radar shows the speed off the racquet, and a served ball lands at roughly 75% of that.

Is momentum in tennis real?

Claims like "five points in a row, that's momentum" rest on tiny samples. It's a myth Sackmann and Kovalchik keep dismantling.

What this doesn't cover

The 70% and 66% split is a secondary write-up of O'Shannessy's counts, not a peer-reviewed table, and it should be scoped by tour, surface and era. Match Charting Project data is licensed for non-commercial use. Affiliations and careers change, so check them at the time you quote them.

Sources

Brody, Cross & Lindsey, The Physics and Technology of Tennis (2002)
Elliott, Marshall & Noffal, Journal of Applied Biomechanics 11 (1995)
Jeff Sackmann's GitHub repositories and Tennis Abstract
Stephanie Kovalchik, On the T
Tennis World USA: The First 4 Shots
Hawk-Eye Innovations

Know the gameHow does Hawk-Eye work in tennis, and how accurate is itHawk-Eye works by filming the ball with about ten high-speed cameras, crossing their sight lines to fix its position frame by frame, and fitting a flight path through those points. The bounce mark is computed from that path, not photographed. Its claimed mean error is about 3.6 mm, inside the 5 mm tolerance the ITF requires.Know the gameWhich tennis stats actually predict who winsThe tennis stats that track the result are the quiet ones: second-serve points won, what happens by the fourth shot, and the few points with real leverage, like break points. Aces, winners and errors describe the last shot, not why the match was won. About two points in three end within four shots, and the box score never tells you that.Know the gameWhat is Elo in tennis, and why it beats the rankingsElo in tennis is a rating that predicts who would win a match, updated after every result. The ATP and WTA rankings reward results over 52 weeks, with bonuses by round and tournament, so they measure what you entered and won. Elo measures strength. On the 2019 Davis Cup finals, Elo called 72 % of matches right and the ATP ranking 60 %.Know the gameHow long are tennis rallies, and what to practiseMost tennis points are short: about two points in three end within four shots, and more than 70 % on grass, and the most common rally length is one shot. By surface the share runs from 65% to 77%. That means the serve, the return and the next ball decide most points, so they're worth a bigger share of your practice time.