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