How BuzzFeed News Used Betting Data To Investigate Match-Fixing In Tennis

With GIFs.

I’m John Templon, an investigative data reporter for BuzzFeed News. I spent the past 15 months analyzing tennis betting data to see if I could figure out whether players were fixing matches.

Jared Harrell / BuzzFeed News

(You can read that full story here.)

I don’t play tennis. I’m a numbers guy. And my first inkling that something was amiss in the world of the "gentleman’s game” came from a statistics journal.

Jared Harrell / BuzzFeed News

A professor of sport management at Florida State teamed up with a professional tennis gambler, and they published a study estimating that professional tennis players likely "manipulated or outright fixed" 23 first-round matches in professional tournaments every year. That's about 1%. But the report did not look at individual players. And they only looked at matches between 2011 and 2013. So….

I crunched a huge amount of betting data, looking for signs of players who might be throwing matches.

Why look at betting data? Well, the main point of fixing a match is to make money off the betting. In a normal match, some people bet that one player will win and some people bet on the other, based on the odds that bookmakers have set. But if huge bets start pouring in on one side, that looks very much like a sign that some gamblers think they know more than the bookmaker about how that match is going to go. Perhaps they know one player is going to tank.

I analyzed data from 26,000 professional matches from 2009 to 2015.

Jared Harrell / BuzzFeed News

Which is really a lot. Bookmakers adjust the odds depending on how people are betting on a match. So I looked at the odds that seven major sports books initially offered for each match, and then compared them with the final odds, to see how far they had shifted.

Then, I selected matches where the odds moved — a lot. As in, more than 10 percentage points.

This happened in about 11% of all matches. There are all sorts of possible reasons for that kind of movement. Maybe a player was injured while he was warming up, for example, and people shifted their bets accordingly. But maybe some people had inside information, like knowing that a player was going to deliberately lose his match.

Bettors seemed to be wagering money heavily against certain players. And then some of those players lost their matches far more often than their opening odds would have led anyone to expect. Curious...

Jared Harrell / BuzzFeed News

To estimate how often they should have been expected to lose, I ran 1 million computer simulations per player. (To learn more, you can read our detailed methodology.)

Through this analysis, I identified 15 players who lost heavy-betting matches startlingly often.

Four players showed particularly unusual patterns, losing almost all of these matches. Given the bookmakers' initial odds, the chances that the players would perform that badly were less than one in 1,000.

The analysis was undertaken with only the betting information that is publicly available. Tennis authorities and betting houses have access to much finer-grained data, such as the accounts placing bets, as well as forensic evidence such as phone data and bank records. Without access to such information, it is impossible to know with a sufficient degree of certainty whether these suspicious patterns are indeed the result of match fixing. For this reason, BuzzFeed News has decided not to name the players.

For one player, I identified 16 matches for which bookmakers revised his odds of winning downward by at least 10 percentage points.

He lost 15 of the 16 matches, including some in which he started as a heavy favorite.

Jared Harrell / BuzzFeed News

Betting patterns alone aren't proof of fixing. Players can underperform for all sorts of reasons — injury, fatigue, bad luck — and sometimes that underperformance will just happen to coincide with heavy betting against them. But it's extremely unlikely for a player to underperform repeatedly in matches on which people just happen to be betting massive sums against him.

In fact, according to my simulations, this player would have been expected to lose this many of the matches (or more) less than 1 in 7,500 times, based on bookmakers' initial odds.

In one tournament in 2010, a bookmaker started the player with a roughly 69% chance of winning his first match. But in the hours before that match, his odds were cut to just 47%.

Jared Harrell / BuzzFeed News

He lost in two sets.

Again, it's impossible to know whether this match was fixed. But these patterns are very strange and, well, improbable. And it's not just these patterns. To learn more about possible match-fixing in tennis read the full BuzzFeed News/BBC investigation.