Major League Baseball could obviously never have a team go undefeated (actually, I found out it did happen in 1869, so from now on let's just go with the live-ball era forward) because of the large amount of games played each season. The best in recent history were the '01 Mariners, who won close to 75% of their games. So on any given day the worst team can, and fairly often does, beat the best team.

To me it seems like the closest a team could ever get to "undefeated" would be to win (or at least tie?) every series in the season. For example, taking 2 out of 3 games against the Red Sox, then 3 out of 4 against the Orioles, and so on. In this specific case total wins isn't relevant.

As an example I just quickly went through the wins-losses for the 2015 Cardinals. They played in 51 different series. Of those they won 32, lost 15, and tied 4. Depending on how you look at it their percentage of series won would be .638, or their percentage of series not lost (wins + ties) would be .706. In either case that percentage is not too different than the winning percentage of total games .617 (100 wins). So I'm not too surprised, because this is the type of data I would guess is pretty normal.

What I'm curious to know is about anomalies such as a team winning ~60% of their games while managing to win 90%, or more, of the series played by remaining consistent. The thought of tie-breakers sparked this curiosity.

I'm calling this "series-wins" for a lack of better term. Is there an actual statistic for this? Or better yet is there a resource that keeps track of this? I have tried searching, but can't seem to find anything.

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    Depending on how you define "Major League Baseball", you may want to refer to my answer here - a professional baseball team did manage an undefeated season, admittedly in 1869. Perhaps edit your question to specify which years you're interested in? – Philip Kendall Sep 22 '16 at 14:07
  • The accepted answer to that question basically implies the answer to this one as well. If you have a 3-game losing streak, at least two of those games must occur in one series. Unless that series happens to be a 4-game series (uncommon), the 3-gamer involves a series loss. Verifying that those teams did, in fact, lose a series at some point in the year is left as an exercise for the reader :) – chepner Sep 22 '16 at 15:26
  • @PhilipKendall thanks for the insight about the undefeated season. I wasn't aware of that, so yeah, they clearly would have won every series. I also updated my post to define "Major League Baseball" by the live ball era until now. – Ben Harrison Sep 22 '16 at 17:51
  • @chepner I see your point, but there are still questions around that. If the shortest "Longest Losing Streak" were 3 games, that team could still theoretically have 20 of them. Or more likely they have a bunch of 1 & 2 game losing streaks. Those could wrap around a series; lose game 1, win game 2, lose game 3, lose game 1 of the next series, etc. Also I did a "reader exercise" for the '15 Cardinals. Please see my edit for details. – Ben Harrison Sep 22 '16 at 18:01
  • Your edit poses a much more general question that your original question. – chepner Sep 22 '16 at 18:05

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