The Summer of Jeff

Home-court in tennis: Update

Posted in tennis by Jeff on September 9, 2010

In yesterday’s post, I presented some research on the degree of home-court advantage in men’s tennis.  Much of my reasoning was correct, but my dataset was flawed.

My intent was to exclude matches in which at least one of the players received a wild card into the tournament.  This is an obvious selection bias when it comes to home-court: Wild cards are generally local heroes; they are also often players who tournament organizers think are better than their rankings reflect.

In processing the data, I got rid of some of the WCs, but nowhere near all.  Of my sample of 666 matches, 222 (yikes, this is getting creepy) had a wild card in them.  So that leaves a sample of 444 matches from 2009.

Adjusted conclusions

Of the 444 matches, the home player won 266, or 60 percent.  Using my algorithm for predicting the outcome of each match, the home player should have won 227–just barely more than half.

In other words, my surprise yesterday (and ensuing convoluted explanation) was purely a result of including the wild cards.  On average, the home player and his opponent were equally matched.

The new conclusion is that players are about 17 percent more likely to win when they are in front of their home crowd and their opponent is not.  To include this in my algorithm, multiply the home player’s ranking points by 1.5.

A note on wild cards

We can draw some obvious conclusions about wild cards, too.  If removing WCs from the sample means the home-court advantage goes down, the home-court advantage for WCs must be bigger.  And since the majority of WCs are playing in their home country, we may be able to say that there is some sort of “WC advantage.”

As I’ve suggested, it isn’t so much that wild cards have an advantage, it’s that a wild card’s ranking points are much less likely to accurately reflect the player’s skill level.  To take just two examples, David Nalbandian and James Blake both received several wild cards this summer.  Both players are returning from injury.  My algorithm sees them as players outside of the top 100, but obviously, when healthy, they are far better than that.

(That’s one reason I’m interested in the notion of ‘peak ranking.’  If Pete Sampras came out of retirement tomorrow, he’d almost instantly be able to beat players in the top 50, if not the top 20 or even top 10.  But it would be some time before his ranking reflected that.  We’ve seen this phenomenon in the women’s game with Kim Clijsters and Justin Henin.)

There’s a lot more to study here on another day.

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Home court advantage in tennis

Posted in tennis by Jeff on September 8, 2010

There’s some sort of home-court or home-field advantage in every sport, so why not tennis?

To test the hypothesis, I looked at all ATP-level matches from 2009.  I excluded qualifiers and matches decided by a walkover or retirement.  I also excluded matches where one of the players received a wild card into the tournament.

Limiting the field to matches where one player was on his home country’s turf and the other was not, that leaves us with 666 matches. (Maybe I should stop now.)  All else equal, if there was no home-court advantage, we’d expect 333 wins from the home player.  In the event, the home player won 358, or 53.8 percent of the matches.

Is all else equal?

Over the course of nearly 700 matches, we might expect everything to wash out.  We would be wrong.

Using my simple algorithm for predicting the outcome of matches using ATP ranking points, we can calculate the likelihood that the home player would have won each match.  For instance, when John Isner (565 points) played Christophe Rochus (1248 points) at Indian Wells last year, the ranking points gave Isner a 29.5 percent chance of winning.  It turns out that Isner beat the odds and won the match.

As I said a moment ago, if all else was equal, the home player would have won 333 matches.  But all else wasn’t equal.  The average visiting player was considerably better than the average home player.  Based on my calculations for each match, home players should have won only 288, or 43.2 percent.  Remember, they won 358, or 53.8 percent.


I’m not sure what’s more surprising: the apparent magnitude of home-court advantage, or the relative weakness of the home players.  (Remember, I excluded wild cards, so these are all guys who earned their way into the draw.)

Let’s spend a moment on the latter.  One possible explanation is home-court advantage in qualifying.  For instance, Jesse Witten (197 ranking points, about 250th in the world) fought his way through qualifying to the 3rd round of the US Open last year.  There are even more extreme examples with the occasional player who is wildcarded into qualifying, and makes the main draw.  An example is Milos Raonic, who with 40 ranking points (about 700th in the world) qualified for the main draw in Montreal.

Another possible explanation is that mid-level players (think 50th – 150th in the world) are more likely to play closer to home when given a choice.  For many weeks of the year, there are multiple ATP tournaments, and in weeks where there is one (non-major) tourney, many players take a break.  So an event in France may be more likely to attract French players to fill out the draw, even if the mix of seeded players is similar to that of non-French tournaments.

Quantifying home-court

As we’ve seen, home players had a huge advantage in ATP matches last year, winning about 24 percent more often than we would otherwise expect them to.

One way to incorporate that in my algorithm is to multiply the ranking points of the home player by about 1.7.  In the Isner-Rochus example above, that adjustment would have given Isner a 43 percent chance of winning.

To take another example, without factoring in home-court, Sam Querrey had a 53.3 percent chance of beating Stanislas Wawrinka yesterday.  Considering home-court, that number is 67.2 percent.  (Of course, Querrey lost.)

One big objection

A final thought.  As I’ve mentioned in just about all of my posts on tennis, surface is not considered in any of my analysis.  That’s a function of the ATP rankings, which also do not consider surface.

Home-court advantage may in part reflect something literal about the “home court”–that it is the player’s favored surface.  Many more European players grow up on clay courts, and sure enough, that’s where most of the clay-court tournaments are.  Querrey or Isner is much more likely to win a hard-court match than a clay-court match, whether it’s in Washington or Bangkok.

So when a player is competing in his home country, he is more likely to be playing on his favored surface.  That doesn’t erase the validity of my results, it just suggests that they could be broken down further.  Maybe a quarter of the home-court effect is really a surface effect, while the other three-quarters is due to the home crowd and home cooking.  Eventually, we’ll find out.

If relegation met baseball

Posted in baseball analysis by Jeff on September 7, 2010

One tidbit jumped out at me from the book Soccernomics.  Fans turn out for games that matter. (Big insight, right?)  The category of “important games” of course includes contests such as those that help determine who makes the playoffs.  But in European soccer, fans also turn out for games that help determine which teams are relegated, and which will take their places.

For the uninitiated, here’s a quick background on relegation.  There are four leagues in British soccer.  At the end of each season, the worst performing teams in each league are demoted to the league one level lower, while the best performing teams are promoted to the league one level higher.  It’s kind of like promoting the Triple-A champions to the major leagues, but without the problem of team affiliations.

So, British soccer has stumbled upon what Major League Baseball might view as the holy grail: a way to get fans to come see the worst teams in the league.  Not every MLB team can have Trevor Hoffman chasing his 600th save.

Introducing relegation stateside

How would relegation work if applied to North American baseball?  It would require some massive changes to MLB’s structure, probably radical enough that we can be sure they’ll never happen.  Let’s consider it anyway.

First off, it’s important to throw away the metaphor of “promoting Triple-A teams to the majors.”  Unless we go back to the pre-Branch Rickey days of unaffiliated high-level minor league teams, that just doesn’t work.  Clearly, we can’t have the Scranton-Wilkes Barre Yankees competing with the New York Yankees.

That means that if we’re going to have leagues of different levels, we have to carve them out of the current 30 squads.  Let’s say we take the 10 worst teams (by won-loss record) at the end of some season, and with them, form the “Challenger League.”  Leave the current American League and National League in place, and give each league a two-division structure.

Each team would play an unbalanced schedule, primarily playing teams within their league, but playing a fair amount of interleague games.  We may be bored with Blue Jays-Phillies matchups, but I suspect the relegation aspect would spice things up.  Sure, AL/NL teams would be favored over Challengers, but they wouldn’t win every time, and Challenger League fans (like fans of British soccer) could even gloat over losses, if they were close enough.

A(nother) new playoff structure

At the end of each year, two (or maybe four) teams are promoted from the Challenger League to take the places of the worst-performing teams in the AL and NL.  Thus, not only do the pennant races matter in the Challenger League, but the cellar races matter in the AL and NL.

The current playoff structure could be kept almost intact.  Award playoff spots to the winning teams in each division: 2 AL, 2 NL, and 2 CL, then give a wild card to the best remaining team in the AL and NL.  Maybe the CL division winners wouldn’t “deserve” a spot, but what the hell.  Worst case scenario, it’s a “bye” for the top-seeded team in each league, and it emphasizes the temporary nature of relegation.

The toughest aspect of managing relegation from year to year is keeping the leagues balanced and travel schedules under control.  Occasionally, a team would have to switch from the AL to NL, or perhaps one would be demoted from the AL, only to come back in the NL.  The geographical balance of each league would be temporary; perhaps it would be best if each league’s East and West divisions were allowed to vary between 4 and 6 members.

Relegating the traditionalists

Introducing relegation would take a huge shift in a sport that isn’t very good at accepting huge shifts.  None of the individual steps (except for the promotion/demotion itself) is that huge: We’ve already seen league realignments, division realignments, interleague play, and changes to the playoff system.

But consider the counterpoint.  If MLB could sell the fans on this, 20 or more teams would in a race for something all year long.  For Yankees fans, it would mean fewer Yankees-Orioles games.  (Until the O’s got good again, anyway.)  For Orioles fans, it would mean a shorter time horizon before making the playoffs through the Challenger League.  Teams like the Brewers and Blue Jays could maintain fan interest with their yearly battle to avoid relegation.

It’s not going to happen.  But it sounds like fun.

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