Yes, March Projections Matter in September
Back in March, all we had to look at for the 2021 season was projection; we’re now on the cusp of September, with just over 80% of the games already played. To the consternation of a percentage of fans, projections on sites like this one look unreasonably grumpy to teams like the Giants, who have played above their projections in 2021. It’s undeniable that they have been off for teams, which is something you should expect. But are these computers actually wrong when predicting middling play from these high-achieving surprises going forward?
The Giants, in particular, have already outperformed their original preseason projections by somewhere in the neighborhood of 10 wins. With a month to go in the season, it wouldn’t be a total surprise if San Francisco ended up with 25 more wins than the predictions. Yet our assembled projections only list the Giants with an expected roster strength of .512 over the rest of the season. Using ZiPS alone is sunnier but also well off the team’s seasonal pace through the end of August.
| Team | W | L | GB | Pct | Div% | WC% | Playoff% | WS Win% |
|---|---|---|---|---|---|---|---|---|
| San Francisco Giants | 100 | 62 | — | .617 | 52.8% | 47.2% | 100.0% | 13.6% |
| Los Angeles Dodgers | 100 | 62 | — | .617 | 47.2% | 52.8% | 100.0% | 12.8% |
| San Diego Padres | 84 | 78 | 16 | .519 | 0.0% | 12.6% | 12.6% | 0.3% |
| Colorado Rockies | 73 | 89 | 27 | .451 | 0.0% | 0.0% | 0.0% | 0.0% |
| Arizona Diamondbacks | 73 | 89 | 27 | .451 | 0.0% | 0.0% | 0.0% | 0.0% |
Yes, ZiPS projects the Giants as the slight favorite to win the NL West now, but that doesn’t take a lot of mathematical courage given that they’re already in first place with most of the season done. With the help of a little math, you can see that the computer projects San Francisco to go just 16–16 the rest of the season; to be more precise, ZiPS thinks the Giants have a roster strength that indicates a .521 winning percentage with their average opponent for the rest of the season having a .520 roster strength, resulting in a mean projection around the .500 mark. That’s up quite a bit from the preseason, when ZiPS thought the Giants were a .467 team with a .502 schedule, ending up with a 75–87 preseason estimate. But it almost feels a bit disrespectful to the team leading the league in wins for most of the season.
So why are projections so grumpy? In a nutshell, it’s because they’re assembled based on empirical looks at what baseball’s history tells us, not (hopefully) the aesthetic valuations of the developer. And in the baseball history we have, seasonal projections do not become this all-powerful crystal ball when it comes to projecting how the rest of the season goes.
Dan Szymborski