Playoff Formats and the Marginal Win

In the weirdest year of baseball history so far, 2020 featured a gigantic playoff field introduced right as the season began, turning a 10-team postseason into a 16-team format. Changing the basic structure of awarding the sport’s championship with no advance notice would have been an odd choice in a normal season. But given the 102-game reduction in the league’s schedule and its resulting small sample size season, it kind of made sense. When the decision was made, it wasn’t a surety that there would even be a season, to the point that people would have been happy if extra-inning games were decided by closers riding ostriches and jousting.

Before the World Series was even completed, commissioner Rob Manfred expressed the league’s desire to keep the new format in a normal season. The players need to agree to changes like this, of course, and that permission wasn’t granted after all MLB offered in exchange was a universal designated hitter. One of the concerns, not officially made public, is that a playoff system that is more of crapshoot will further reduce the already eroded incentives for teams to spend money to improve their rosters. That’s hardly a shock; at the 2020 trade deadline, 10 teams already had projected playoff probabilities above 97%. Combine that with the absence of the normal advantages afforded to higher seeds, and you had a trade deadline that saw only a single team, the San Diego Padres, aggressively improve, and even their moves were almost certainly made with an eye toward 2021 and beyond.

So what is the ideal playoff system? That’s a difficult question, one that’s impossible to answer to everyone’s satisfaction. I can only answer for myself, and for me, there are a few requirements that are particularly important. Basically, I want a system in which regular-season performance matters, thus maintaining one of the core aspects of the game. I also want a playoff system that more heavily awards quality over randomness without making the result a preordained one. The more a championship is decided by randomness, the less incentive there is for teams to innovate and invest.

To keep people interested in baseball’s long regular season, the wins have to actually matter. So what is the value of an additional win under various playoff formats? To answer this, I reconfigured ZiPS to run using four new playoff formats: a 14-team playoff system with byes for the top teams in the first round, a 16-team playoff system like last season, a four-team playoff system with the top two teams advancing, and the no-division format in use before the 1969 season. I then ran 31 simulations for each playoff format, first to get the baseline World Series win probability, then adding a single win’s worth of strength to each of the 30 teams in order. After writing three new models and running a million seasons in 155 separate simulations, I’ve got some hard data I did not previously have. Also, I think I hate numbers and never want to see one again!

Let’s start with the current format:

By adding a single win, the average team gained 0.44 percentage points of World Series championship probability. Considering gains of at least 0.1 percentage points significant — since that’s what we normally round to — 20 teams saw movement by making them one win stronger. Somewhat arbitrarily, I imagine 0.5 percentage points as being major gains; 12 teams meet that threshold. Where we set these lines doesn’t necessarily matter in that we’re simply looking at relative changes due to format. Under the current format, the best teams all see significant benefits of adding a win thanks to division winners not having to play the high-stakes Wild Card game.

Next up, 2020’s format:

Naturally, baseball’s best teams take the biggest overall hit, with the Dodgers losing nearly a third of their simulated championships. That the Dodgers actually did win in 2020 is one of those little practical jokes that history likes to pull, with the most random playoffs in history resulting in the winningest AL and NL teams making the World Series. It would be a mistake to assume predestination here; it only requires changing a few plays last October to get the 29-31 Houston Astros into the World Series.

More teams see gains in playoff probability, with 25 teams now making that 0.1 percentage-point threshold. But now, not a single team meets the 0.5 percentage-point mark. With no bye for division winners, adding a free agent who improves the roster by a win suddenly has less than half the value for quality teams in tight division races like the Dodgers, Padres, Yankees, and Mets. Teams at the bottom, however, improve but remain long shots.

So, let’s restore the divisional advantage with one of MLB’s proposals, a 14-team format that leaves the top team in each league with the ability to skip the Wild Card round:

Under this blueprint, the average team’s World Series probability gains 0.35%, less than the current system’s 0.44%. Still, by giving a significant advantage to each league’s best teams, there’s a real motivation not to coast into the playoffs at 89 wins. Twenty-two teams pass the significant gain line, and the number of teams passing the major gain one goes back to 11 from zero.

Let’s go really old-school and look at the playoff format that dominated before the divisional era: two leagues, with the best team in each league going straight to the World Series:

The average gain is the highest so far, with 0.67 percentage points per team. The gains, however, are limited to only a very few teams, with the break point somewhere around 85 wins. One can argue that this isn’t necessarily healthy for baseball, either. Teams like the Dodgers see larger gains by adding free agents, but those individual free agents would have a lot fewer suitors despite the larger average improvement. Auctions require bidders! This is likely the best playoff format for crowning the best team but may not be a healthy one for the game for various other reasons.

As the last playoff format to look at today, I ran a modified version of the divisional era format. Rather than making up new divisions — there are teams in different leagues and two teams that did not exist during the two-division era — I simply looked at the two best teams in each league.

Not surprisingly, this one comes smack-dab between the 10-team system and the old-school one. With 17 teams at worse than 100-to-1 to win the championship compared to 13 today, it has some of the same problems as the pre-divisional system, though they aren’t quite as severe.

Here’s the quick-and-dirty summary for the five formats we looked at.

So, what does this all mean? One can make the argument that whether by design or dumb luck, MLB has stumbled into a reasonable playoff configuration. The regular season still matters and while a third of the league makes the playoffs, there are real benefits to winning the division.

We’re far more likely to get more teams in the playoffs than fewer going forward, but I think these numbers demonstrate some of the risks involved of simply shoving more teams into October. Having more teams make the playoffs doesn’t have to destroy the regular season or eviscerate the value of adding a Mookie Betts or a Yu Darvish. But it will have to involve the league designing a postseason that not only gives more teams hope but also makes teams actually care whether they win 90 games instead of 88, or 98 instead of 96. This is absolutely necessary because of how even teams are, relatively speaking. The NBA postseason works with 16 teams because low seeds mainly get destroyed by the top seeds. No MLB team can be the Jordan-era Bulls or peak Warriors.

Three professors, Michael J. Lopez, Gregory J. Matthews, and Benjamin S. Baumer, looked at this specific issue a few years ago and estimated that to match the NBA’s playoff history of the team with the better record 80% of the time, baseball would need to have best-of-75 series. I don’t think I need to go into why that is impractical.

I think that for a larger playoff field to be a good idea requires MLB to continue to re-think what kind of advantages can be given to the better teams. The bye was a clever idea, but there are limitations of how many byes you can give top teams before you’re almost penalizing them by making them cool their jets for weeks. That likely makes a straight-up application of the KBO’s gauntlet also a non-starter. What it might take is for MLB to explore lopsided playoff series. If you’re going to give a chance for a 78-84 team to knock off a 105-win team, you need to think of a bigger hurdle than winning two of three games. Why not require a four-game sweep?

If expanding the playoffs is going to mean more to the owners than simply a way to fatten their wallets and thin those of the players, some creativity will be needed. We’ll see.