MLB All Star Break Report: Statistical Predictions

Teams that outscore their opponents, on average, should win a lot of games. Likewise teams that get outscored on average should lose most of their games.

This is a very simple concept, and I will use it to analyze the MLB season before the All-Star break and make some predictions for the rest of the year.

I have used the run differential (total runs scored minus total runs allowed) in a linear regression to try to explain the win percentage of each major league team.

In general, it would make sense that teams with the highest positive run differential would also have the highest winning percentage. And vice versa; that teams with the highest negative win differential would have the lowest win percentage. Teams with a run differential around 0 should have a win percentage around .500 because, on average, they should win just as many games as they lose.

Of course this would never work out in real life. In addition to random variation and luck, some teams also just perform really well in close games while others do not. Some teams are more over-matched by the better teams and some teams are better at pounding the bad teams.

However, I propose that teams with a run differential much higher than their record would suggest have a strong potential to find more success in the remainder of the season because they have shown the ability to consistently outscore opponents. The reverse is also true; teams that have a win percentage much higher than their run differential would indicate (teams that are getting “lucky”) a potential for a less successful second season.

Under these assumptions, I interpreted the results from my regression and will exhibit them below. The graph of predicting win percentage from scoring difference can be seen at the top of the article.

I was very pleased with how the graph turned out for several reasons. The regression equation is:

Winning Percentage = .500 + .000941(Run Differential)

This says that for every run a team scores more than their opponent, their winning percentage will increase by .0941%. It is a very good sign that this is a positive number, or else scoring more runs than you’re opponent would be a bad thing.

The equation also says that a team with a run differential of exactly 0 would be expected to have a winning percentage of .500. This makes sense and I was very pleased that this worked out exactly. It is a good sign that run differential is a good predictor of winning percentage.

Finally, the R-squared value for the regression was 71.3%. This means that 28.7% of the variability in team winning percentage is left unexplained by only using run differential. This makes sense from my discussion before; some teams get lucky and some teams also have a knack for winning or losing close games. However, 71.3% is fairly high for only using one variable. While run differential is not necessarily a good precise predictor for win percentage, it is a very reasonable approximation.

Now that I feel fairly safe with my assumptions, here are the interpretations for the results.

First, the most interesting teams on the graph are ones that fall far from the regression line. Teams underneath the line have won fewer games than their run differential would suggest (“unlucky”), and teams above the line have won more games than their run differential would suggest (“lucky”). The further a team is from the line, the more lucky or unlucky they have been. Note that I use the term lucky and unlucky very loosely here, as there is certainly some skill involved in winning close games.

Based on the results, here are ten teams that should expect the biggest change in winning percentage for the rest of the season. The over-achievers will likely perform worse, and the under-achievers should do better.

Top 5 Over-Achievers

1. Angels

2. Marlins

3. Twins

4. Rays

5. Rangers

Top 5 Under-Achievers

1. Indians

2. Braves

3. Mariners

4. Phillies

5. Blue Jays

Now I will break down the MLB pre-All Star break season, still based on my results, for each division. I have calculated a modified version of the standings assuming that win percentage only depends on scoring margin. I included the original standings for comparison. Teams with significant changes in standings have strong potential to have differing success for the rest of the season.

AL East:

Team	Modified Standings	Original Standings
Red Sox	-	-
Rays	5	.5
Yankees	7	6
Blue Jays	7	9
Orioles	10	10

The biggest flag here is the Tampa Bay Rays. They could be much further behind the Red Sox now, so don’t be surprised to see them fall further behind after the All-Star break.

Also, look out for the Blue Jays in the second half. It will be difficult for any team to dethrone the Red Sox, but the Blue Jays could have a strong run and at least contend for the Wild Card.

AL Central:

Team	Modified Standings	Original Standings
White Sox	-	-
Twins	6	1.5
Indians	7	13
Tigers	7	7
Royals	13	12

While many consider the White Sox season to date to be a fluke, the numbers suggest otherwise. They have a comfortable division lead in the division standings, so I wouldn’t expect them to fade very much.

After some small glimmers of hope, Royals fans should expect another very poor end of the season results.

The Tigers still need to improve a lot to make a run at the division, and the Indians could also move up the standings a lot in the second half of the season.

The Twins may have already played their best baseball of the season, but could still hang around for a while.

AL West:

Team	Modified Standings	Original Standings
A’s	-	6
Angels	4	-
Rangers	8	7.5
Mariners	11.5	20

The modified standings show a huge reversal at the top of this division. Even though the A’s just traded away their ace, the Angels should be a lot more worried about being caught than most people think.

The Rangers have over-achieved so far, so don’t expect them to make a serious run towards the playoffs.

Also, the Mariners aren’t quite as bad as their record would suggest. They could win a lot more games in the second half and build some momentum going into next season.

NL East:

Team	Modified Standings	Original Standings
Phillies	-	-
Mets	3.5	.5
Braves	3.5	6.5
Marlins	9.5	1.5
Nationals	17.5	16

Like the other Florida team that had a lot of first half success, the Marlins should continue to slide in the standings.

The Phillies look like they are going to be tough to beat this year, but they will have to watch out not only for the Mets but the Braves as well.

The Nationals are flat out bad and should easily secure the worst record in baseball after the All-Star break.

NL Central:

Team	Modified Standings	Original Standings
Cubs	-	-
Cardinals	7.5	4.5
Brewers	8	5
Astros	13.5	13
Reds	14	11.5
Pirates	15.5	12.5

From these results, the Cubs look to have the safest division lead out of all the division leaders. Every team in this division has actually over-achieved, but the Cubs and Astros have over-achieved the least.

The Brewers may be the only team with hope of making a run at the Cubs after adding C.C. Sabathia to the top of their starting rotation.

NL West:

Team	Modified Standings	Original Standings
Dodgers	-	1
Diamondbacks	.5	-
Giants	6	7
Rockies	9	8.5
Padres	9	10

Amazingly, all of these teams under-achieved in the first part of the season. That’s a very good sign considering how bad these teams have been so far. No team has a winning record.

The Dodgers and Diamondbacks should have a very close race for the division lead, and the Giants will be looking to make it a three-way race.

The defending N.L. Champion Rockies might need another miraculous win streak to have a chance to defend their title.

Of course it is impossible to predict what is really going to happen in the future, but hopefully this analysis provides some good insight for what to expect. It will be interesting to see how well these discrepancies match up with what actually plays out, and I will be sure to keep an eye on that.

For those interested, detailed MLB Standings can be found here. I found it interesting to look at the probabilities for each team to make the playoffs, win the division, and win the Wild Card.