Is the Pirates 20 season losing streak over?

The Pittsburgh Pirates have finished the last 20 seasons with more losses than wins. This is the longest such streak in any of the four major American professional sports leagues (NHL, NBA, MLB, NFL). The streak is likely to end this season, however, because the Pirates are tied for the best record in baseball. As it stands now, the Pirates are 48-30 which earns them a .615 winning percentage through just shy of half the season. I wondered whether any team with such a good first half finished with a losing record. Unfortunately some quick googling didn’t answer my question, so I resorted to querying the retrosheet gamelogs data I have stored on my computer1.

It turns out that there are four teams in the history of baseball2 with .600 or better records at the midpoint of the season3 who finished without a winning record. These four teams are:

Year Team Mid W Mid L Mid W% Full W Full L Full W%
1890 Philadelphia Athletics 41 22 .651 54 78 .409
1889 Cleveland Spiders 40 24 .625 61 72 .459
1977 Chicago Cubs 48 29 .623 81 81 .500
1905 Cleveland Indians 46 28 .622 76 78 .494

As you can see, two of the teams, the Philadelphia Athletics and Cleveland Spiders are truly ancient. They both experienced horrendous second halves, ending well south of .500. I doubt those teams resemble modern teams so I’m not sure there is much of a lesson to draw from them. One of the remaining teams, the 1977 Chicago Cubs, finished at exactly .500 which would technically end the Pirates losing streak, but would hardly feel satisfying. All four teams are drawn from the 366 teams with .600 records at the midpoint. Therefore, almost 99% of .600 teams finish with winning records. This analysis suggests that Pirates have an extremely strong chance of ending their streak.

Unfortunately, the Pirates are worse by many measures than the typical .600 team. In particular, the winning percentage one would predict from the runs they’ve scored and allowed is .557 not .6154. For math-phobic Pirates fans, let me give you one anecdote to try to convince you of the importance of expected winning percentage. The Pirates have suffered late-season collapses in each of the past two seasons and their pre-collapse expected records were much worse than their actual records in both seasons. This thought-process led me to a second analysis which looked at the second half records of teams that were similar to the Pirates at mid-season.

There are 262 teams with mid-season expected winning percentages within .015 of the Pirates’. Here’s a histogram of their second-half performances:
The distribution roughly matched my expectations. The vast majority of teams won between 40% and 70% of their second half games. The Pirates need to win at least 34 more games to finish with a winning record. This requires a .404 winning percentage for the rest of the season. 10 teams finished with records at least that poor, which suggests the Pirates still have an almost 4% chance of extending their losing streak. I suspect that percentage is too high for Pirates fans to feel comfortable yet. Sorry to disappoint you!

Let’s finish on a much happier note. According to the same analysis, the Pirates have a better chance of winning 105 games, virtually guaranteeing a playoff appearance and very likely a division win, than extending their losing streak. The 12 best teams in my sample6 completed their seasons with .675 or better records, which would yield 105 wins for the Pirates. In 2010, the Pirates lost exactly 105 games to extend the losing streak to 18 seasons. From 105 losses to 105 wins in 3 seasons — THAT would be some story. Certainly a happier one than a 21 season losing streak.

1. Yes I am that kind of dork.
2. I excluded any season with fewer than 100 games.
3. 48.1481481% of their season just like the Pirates so far.
4. See Pythagorean expectation on Wikipedia for more information. I used the 1.83 single number exponent for its mix of simplicity of implementation and accuracy.
5. I excluded seasons with fewer than 140 games this time, partly to exclude the ancient teams.
6. I would have chosen the top 10 teams again for symmetry with the losing-season bottom 10, but four teams were tied at exactly .675.


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