How well do playoff teams do that had losing records to .500+ teams during the regular season?

On the Fox game last night, one of the announcers mentioned that the White Sox had only a .390 winning percentage against teams with a .500 record or better. That, they suggested, could be an issue in the playoffs (the Sox were 16-25 entering last night's game in these cases but now they are 18-25 for .419).

The other likely AL playoff teams are doing better than the Sox (all through last night)

Red Sox 33-25

Rays 37-27

Astros 43-23

A's 27-30

I looked at all the playoff teams from 1995-2019 using Stathead, the searchable data base run by Baseball Reference. I found that 59 of the 216 teams that made the playoffs had losing records to teams that played at least .500.

12 of those 69 teams made it to the World Series (20.33%).

38 of the 157 teams that played .500 or better against teams that themselves were .500 or better made it to the World Series (24.2%).

So there is a slightly better chance to make it to the World Series if you can play at least .500 against teams that played at least .500. But it does not seem like a big deal.

The lowest winning percentage against teams that were .500 or better that made it to the World Series was .400 by the 1997 Indians. There was a .420 and two .450 cases (who both won the series, the 2006 Cardinals and the 2010 Giants-5 other teams that had losing records in these cases also won the series). So the White Sox are still on the low side but this season is not over yet.

3 of the 16 teams that played exactly .500 against teams that were .500 or better made it to the World Series.

Update July 19: The teams that played at least .500 against teams that were .500 or better had an average overall winning percentage of .590.

The teams that were under .500 against teams that were .500 or better had an average overall winning percentage of .561.

 

So it is not surprising that playoff teams that played .500 or better during the regular season against teams that were .500 or better are more likely to make it to the World Series than teams that don't because overall they are better.

The Biggest Declines In Winning Percentage For Pennant Winners, 1901-68

The first table has the AL. W-L%1 is a team's pct. the year they won the pennant and W-L%2 is their pct. the year after. All data from Baseball Reference and Stathead.

The 1914 A's had a pct. of .651 and in 1915 it was .283, for a change of -.368

Tm	Years	W-L%1	W-L%2	Diff
A's	1914-15	0.651	0.283	-0.368
Twins	1933-14	0.651	0.434	-0.217
White Sox	1917-18	0.649	0.460	-0.189
Red Sox	1912-13	0.691	0.527	-0.164
Red Sox	1946-47	0.675	0.539	-0.136
Yankees	1964-65	0.611	0.475	-0.136
Orioles	1966-67	0.606	0.472	-0.134
Yankees	1939-40	0.702	0.571	-0.131
Indians	1954-55	0.721	0.604	-0.117
Red Sox	1918-19	0.595	0.482	-0.113

Now the NL.

Tm	Year	W-L%1	W-L%2	Diff
Cards	1931-32	0.656	0.468	0.188
Pirates	1909-10	0.724	0.562	0.162
Reds	1919-20	0.686	0.536	0.150
Dodgers	1916-17	0.610	0.464	0.146
Dodgers	1966-67	0.586	0.451	0.135
Pirates	1960-61	0.617	0.487	0.130
Giants	1913-14	0.664	0.545	0.119
Phillies	1950-51	0.591	0.474	0.117
Dodgers	1963-64	0.611	0.494	0.117
Cubs	1918-19	0.651	0.536	0.115

The 1914-15 A's are the biggest decliners. But that is because Connie Mack sold or traded away some of his best players. Some had jumped to the Federal League and Mack did not want to get into a bidding war.

Important players who were gone in 1915 include Eddie Collins and Frank Baker. SS Jack Barry played less than half the season with the A's. Star pitchers Eddie Plank and Chief Bender were also gone. See SABR bio of Connie Mack by Doug Skipper. 

Many other players and pitchers from 1914 were still there. But their team OPS+ fell from 114 to 87 (114 means you are 14% better than average, 87 means you are 13% below average). Their team ERA+ fell from 94 to 68 (they had been giving up 6% more runs than average and it went to  32 more than average). The + sign also means the numbers are park adjusted.

The next biggest fall is the 1933-34 Senators. A quick look at them shows that their personnel did not change much and did not look especially old in 1934. Maybe I will do a future post to figure out what happened to them.