The National League’s five best teams are clear of their closest playoff competition by a minimum of two and a half games, and each, per FanGraphs, stands a 78% or better chance of making the playoffs with current rosters, something that may slightly understate the probability, as many teams with marginal playoff probabilities (the Cubs, for example) are about to start selling.
So, how likely is it that the NL playoff field is set?
Teams making the playoffs are not independent events. You can’t just multiply the five probabilities together as though you’re drawing cards from separate decks. They play each other. They play each other’s opponents. But without a full-on Monte Carlo simulation model of our own, we can’t get an exact probability of this five-team combination—the Dodgers, Brewers, Mets, Padres, and Giants—being the eventual five to make the field, and there are some pieces we can loosely assume are roughly independent.
For example: division champions.
While there are certainly some scheduling aspects that affect this, for the most part, the three division champions in the National League are independent from one another. This far out from season’s end, the NL East champion likely does not have a strong correlation with the NL Central champion, which means we can probably treat the three divisions as roughly independent.
If we do that, we come up with a 62% chance of the division champions all coming from that set of five, with the Brewers 81.1% likely to win the Central, the Mets 76.5% likely to win the East, and the NL West 100% likely to go to the Dodgers, Padres, or Giants.
The wild card calculation has less independence to go off of, but it’s estimable taken on its own. If any team from the NL East or NL Central takes a wild card, the five will be broken up (if the Mets or Brewers take a wild card, there will be no wild card slot left for the third NL West team). The calculation, then, is just how likely it is a wild card emerges outside of the NL West triad, and given that those teams have wild card probabilities of 78.2% (Padres), 76.0% (Giants), and 27.8% (Dodgers), there’s just 18.0% of the 200% pie left (it’s 200% because there are two wild card teams). That 18.0% is not a straight-up probability that at least one of the wild cards will not be the Padres, Giants, or Dodgers: There are scenarios within that 18.0% block in which both wild cards are not from the NL West. But those scenarios are likely rather rare, and we can assume a roughly 80% probability that the NL Wild Card game is NL West-exclusive.
Combining these, then, gets tricky again, because the Brewers or Mets getting caught is strongly correlated with the Dodgers, Giants, or Padres getting caught. If the two events were independent, the probability would be roughly 50/50 that the playoff field is set (62% times 80% rounds to 50%), but again, they’re far from independent.
That 50/50 number does, however, give us a bottom bar on the range of possible probabilities. The probability, with current rosters (which is what FanGraphs uses for their simulations), is somewhere between 50% and 62%, depending on the wild card/division correlation. Given that correlation should be rather strong, we’re probably looking at something close to a 60% chance the playoff field is set.
Again, though, that’s probably too low. Buying and selling decisions matter, and one would guess that FanGraphs doesn’t have a great way to account for them during this slot of the year in which they’re both 1) rather knowable and 2) rather impactful, two things that are rarely in concert in the baseball calendar. If you call the Reds and Phillies buyers and the rest of the NL sellers, assign each of the sellers’ division championship probabilities to the leader in their respective division, and run these calculations again, you get somewhere between a 58% and a 73% chance the playoff field will hold, again closer to the high end than the low end of the range.
Overall, then, we’ve got probably a sixty or seventy percent chance of seeing these exact five teams in the playoffs. That could rise dramatically over the next few weeks. It probably won’t fall dramatically, barring injury or a surprisingly swift rise and/or stumble. But it’s at sixty or seventy percent, and to be honest, that’s not that closed-off of a race. On July 15th in 2017, two NL division leaders were more than 98% likely to hold their place, with the third at 63%. On July 15th in 2016, Two were at 89% or higher and the NL West had consolidated down to just the Giants and the Dodgers. Even 2018 and 2019 featured a least-probable division leader at two-thirds likely to win the Central on July 15th, and while the Cubs (the team in question) failed to win their division either of those two years, that’s still not an extraordinarily competitive outlook.
What to make of the original question, then? In human terms, rather than numbers? The likelihood of one of the current five playoff teams not making the field in the NL is comparable to that of the Orioles beating the Yankees on a given night. Not likely. But far from impossible.
