MLB Winning Streak Frequency, Sweep Difficulty & More | Mailbag

June 25, 2012 - by David Hess

Mailbag time! We’ve received several questions recently about how often MLB teams win in certain situations, so we thought it would be useful to compile them all here in one place. Enjoy, and please feel free to ask any questions you might have in the comment section!

How often does the money line favorite win, compared to the money line underdog? –Javier R.

Over the past 13,000 or so game, the money line favorite has won 57.1% of the time. However, that obviously varies based on the actual line. If you bin the favorites according to their money lines, here is what you see:

Fave Line Group	Games	Fave Win%
-200 to -415	1048	68.3%
-175 to -199	988	61.1%
-160 to -174	1263	62.3%
-150 to -159	1054	59.7%
-140 to -149	1509	59.0%
-130 to -139	1834	56.7%
-120 to -129	1815	55.3%
-110 to -119	2087	52.1%
-103 to -109	1795	49.9%
All	13393	57.1%

As expected, bigger favorites win more often.

Can you find what the W-L record of a team is during interleague play when the starting pitcher has a win% greater than 75%? –Tee T.

If I just take your question at face value, and don’t add in any requirements for how many games the starting pitcher has pitched in, then teams that fit the bill have won at a 54.3% rate since 2007. If I require the pitcher to have at least 3 wins, then the new win% is 56.3%.

In regular (non-interleague) games, teams starting a pitcher with a 75%+ win percentage and at least 3 wins have a 52.6% win rate. So in this super-simple analysis, the pitcher record seems slightly more important for predicting interleague games.

How often do MLB teams win 2 or more games in a row? I would also like to know often teams lose 2 or more in a row. –Walter M.

There are a few different ways to define this. First, let’s assume you want to know the winning percentage of a team on a 1-game winning streak. That is, if a team has a chance to create a 2-game winning streak, how often do they succeed?

It turns out that teams on a 1-game winning streak have a win% of 50.6% (over about 6500 games). So they fare ever so slightly better than an average team (which by definition wins 50% of the time). Looking at losing streaks, a team that has lost 1 in a row ends up losing their next game 50.2% of the time.

Another way to define this would be to look at every loss, and see if the team won their next two games. In other words, out of all the chances that a team had to begin a 2-game win streak, how many times did they actually do it? The answer to that question is 24.7%. That’s actually slightly less than you would expect by random chance (25%). For losing streaks, the same value is 24.4%, meaning teams follow up a win with 2 straight losses slightly less than you’d expect by chance (25%).

These results make sense — the fact that a team won their previous game means that they are slightly more likely to be an above-average team (and the reverse is true for teams that lost their previous game).

How often does a team trying to complete a 2,3, or 4 game sweep win? This could also be broken up into home/away, favorite/dog, etc. –John C.

As you might have guessed from the answer to the previous question, teams trying to complete a sweep generally win at a bit over a 50% rate (across all scenarios). This table breaks down how often a team that is trying to complete a sweep wins the final game, based on a combination of series length and the other attributes you asked about.

Frequency Of Completing A Sweep, Based On Series Length & Other Factors (2007 to mid-June 2012)

Series Length	All scenarios	Home	Away	Favorite	Underdog
2 Games	51.2%	56.5%	46.2%	54.5%	46.5%
3 Games	50.9%	55.8%	44.2%	57.6%	40.4%
4 Games	55.3%	56.2%	53.6%	59.0%	48.4%

This shows, for example, that road teams trying to complete a 3-game sweep only managed to win the third game 44.2% of the time. Or that Vegas favorites trying to complete a 4-game sweep did so 59% of the time. Keep in mind that the bin sizes here range anywhere from about 50 games to a few hundred, so these values are not going to be very precise — over the long run, some of these will probably change.

How often does the home team win at least one game in a 2 or 3 game series, or one of the first 3 in a 4 game series? Also how about at least 2 games or more in 2,3,or 4 game home series? –Brian M.

From 2007 through early June 2012, the home team won at least 1 game of a 2 game series 76.4% of the time (compared to the 75% you would expect if every game was a coin flip). The home team won at least 1 game of a 3 game series 90.4% of the time (compared to 87.5% in a coin flip league). The home team won at least 1 of the first 3 games of a 4 game series 89.6% of the time (again compared to a random value of 87.5%). And the home team won at least 1 game of a 4 game series 94.6% of the time (compared to 93.8% in a totally random world). The same values for away teams were 72.8% (win at least 1 of 2 games), 83.0% (win at least 1 of 3 games), 82.8% (win 1 of first 3 in a 4 game series), and 90.0% (win at least 1 of 4 games).

Over the same time period, the home team swept a 2 game series 27.8% of the time, won at least 2 games of a 3 game series 56.8% of the time, and won at least 2 games of a 4 game series 74.8% of the time. Those same values for road teams were 23.8%, 43.5%, and 61.5%.