The answer to the above question is the same thing that wins during the regular season. Just play better baseball in general. Get more hits, get more runners on base and hit for more power than the other team. The bottom line is that you need to score and prevent runs. The teams that do the best job of this generally win during the regular season and postseason.
First, let's look at what wins during the regular season. In its 1998 Baseball Scoreboard book, STATS, INC presented some data on which team won regular season games over the previous 5 years. Below are the winning percentages of teams that had the higher stat in a game.
SB per 9 offensive innings .653
HR per plate appearance .653
BB per plate appearance .623
Most strikeouts per 9 defensive innings .543
So the teams with a higher OPS won 85.3% of the games (OPS is on-base percentage + slugging percentage). That stat had the best winning percentage.
What do these numbers look like for the postseason? Below is data from Tom Ruane courtesy of Retrosheet, which covers the years 1960-2004.
SO .442 (that is by batters-for pitchers it would be .558)
Some of the stats don't match up exactly. For example, strikeouts are not on a per inning basis. But it seems that what it takes to win in the playoffs or postseason is about the same as it is in regular season games. The highest winning percentage goes to OPS, just as it does for the regular season. In fact, "out-OPSing" your opponents works slightly better in the post season. You win 86.4% of the time.
None of this tells us how to "out-OPS" your opponents. Is it done with better hitting, better fielding, better pitching or some combination of the three?
None of this tells us how to "out-OPS" your opponents. Is it a matter of better hitting, fielding, pitching, or some combination of the three?
It may be that the offensive and defensive sides are about equally important. To look into this, I checked the adjusted (ADJ) OPS and adjusted (ADJ) ERAs of the winners and losers of postseason series. When OPS and ERA are "ADJ," park effects and the league average are taken into account. These stats are also ADJ for the fact that hitters don't face their own team's pitchers and vice-versa (see either Total Baseball or the most recent Baseball Encyclopedia edited by Pete Palmer who calculated ADJ OPS so it could be directly comparable to ADJ ERA in terms of runs). ERA is, of course, affected by the quality of the fielders. So when I use the term defense below to mean the role that both pitching and fielding play in preventing runs.
The winning team in the LCS from 1969-93 had an average ADJ OPS of 107.2 and an ADJ ERA of 110.04. The losers had 106.4 and 109.04. So the winning team had an average advantage of .8 in ADJ OPS and 1.0 in ADJ ERA. In other words, the winners were not winning because of some great advantage in defense that they did not have in hitting. They won because they were slightly better at both.
Beginning with the 1995 season, an additional round of playoffs was added to accommodate the wild card team in the three-division format. From 1995-2003, the average playoff series winner had an ADJ OPS of 105.8 and an ADJ ERA of 111.6. For the losers, it was 105.9 and 109.4 (World Series games were not included here)[Note 1] So the winner's have a small advantage in defense (2.2) and very slight disadvantage in hitting (-.1) [Note 2].
Notice that from 1969-93, the teams that make the playoffs have ADJ ERAs that are 2.74 better than their ADJ OPS (2.84 for winners, 2.64 for losers). But the winners' edge in ADJ ERA is only .2 more than their edge in ADJ OPS. That is far below 2.74, suggesting that having and edge in defense is less important in the playoffs than during the regular season. A similar story could be told for the 1995-2003 period.
There is a problem with using regular season data to judge a team's quality in the postseason. Injured players may not be available while late season acquisitions might play major roles. So the regular season ADJ OPS and ERA may not truly reflect a team's relative strengths during the playoffs. But this evidence indicates that teams that make the playoffs are well above average in both defense and hitting, perhaps slightly more above average in defense. This carries over into the postseason, with the winner's advantage also being slightly greater in defense.
Sometimes the ability to win 1-run games is sighted as a reason for postseason success. This may not be a factor, either.
Of the eleven World Series winners from 1995-2005, six had higher winning percentages in regular season 1-run games than they did in other games (one of those five was only .006 better in 1-run games than other games). So five, almost half the series winners since 1995, were actually better in non-1-run games than 1-run games. In fact, the average regular season winning percentage in non-1-run games was .601 while in 1-run games it was .586. So, in general, the champs are no better or worse at 1-run games than they are at other games. The 2001 Diamondbacks actually had a losing record in 1-run games. The 2000 Yankees were just 20-18. The 2004 Red Sox were 16-18.
I also looked at the regular season records in 1-run games of the winners and losers of all postseason series from 2001-2005 (including the World Series). The winners of a series had combined record in regular season 1-run games of .571. The losers had .571 as well.
The bottom line: It does not appear that there are any special reasons for winning in the postseason that do not exist in the regular season. It probably helps, in absolute terms, to have better defense just a little more than it helps to have better hitting since the winnerr's edge in ADJ ERA over the losers is a little greater than their edge in ADJ OPS. Getting base runners and hitting for power is just as important. Finally, being good at 1-run games is not especially helpful.
- World Series results are not included because the ADJ OPS and ADJ ERA comparisons are not meaningful. In a World Series, the opponents compiled their regular season stats against very different opponents. So saying that one team has a better offense because it has a higher ADJ OPS may not be right (remember, that ADJ OPS is based on the league average).
- I took the Braves out of those ADJ OPS and ADJ ERA averages to see how their great pitching affected this analysis. From 1995-2003, the Braves had an average ADJ OPS of 99.89 and an average ADJ ERA of 125.44. Their record in playoff series was 9-6. Non-Brave teams that won playoff series had an average ADJ OPS of 107 and an average ADJ ERA of 108.87. The losers had 103.92/105.67. I counted only 6 other teams in this time period that had and ADJ ERA in the 120-124 range. No other team made it to 125 even for one season. So without the Braves, both winners and losers had less of a gap between their ADJ OPS and ADJ ERAs. And the winners edge in ADJ OPS (3.08) was almost the same as their edge in ADL ERA (3.2).