2020 MLB Over/Unders: Good Defensive Teams Continue to Exceed Their Win Totals

If team defense is the most overlooked aspect of baseball analysis, the quality of a team's defensive metrics, in the aggregate, should have a strong correlation to the likelihood of that team going over or under a season win projection.

With the advent of Outs Above Average ("OAA") from Major League Baseball, I wanted to compare that new three-year data sample to Defensive Runs Saved ("DRS"), to see how MLB's latest invention stacks up against the industry leader in defensive metrics.

From 2017-2019, teams who went over their win total finished with an average DRS of 28.5 and an average OAA of 7.3, while teams who went under their win total finished with an average DRS of 6.4 and an average OAA of -3.3.

However, while the averages hold in the aggregate, they aren't necessarily true at the extremes.

In fact, from the chart above, one data point stands out as an outlier – "Under" teams finished at +5.7 in DRS in 2018, primarily because of the league-leading defense of the Arizona Diamondbacks, who fell three wins shy of their 85-win total.

Remove the Diamondbacks from that 2018 sample, and "Under" teams would have finished with an average of -3.2 DRS and -6.9 OAA.

But I would note that their Pythagorean record suggested an 86-win season, which would have placed them in the "Over" category.

When compared to defensive teams of similar quality, the Diamondbacks are an exception.

Good and Bad Defensive Teams

Over the past three seasons, 11 of the 13 teams (85%) who finished in both the top or bottom five by both DRS and OAA, performed as expected relative to their win total.

The only two exceptions? Those 2018 Arizona Diamondbacks, and the 2017 Cincinnati Reds – both of whom should have surpassed their win totals based upon the Pythagorean record.

Since 2017, eight of the top nine defenses by either DRS or OAA surpassed their win totals; two-thirds of the top-10 defenses by DRS surpassed their win totals, and the same number of bottom-10 defenses fell shy of their projection.

At least concerning good defensive teams, the better the defense, the more likely that that team went Over their win total.

The same trend couldn't be applied to weak defensive teams, but the overall sentiment held – and bottom-10 defenses represented an "Under" two-thirds of the time.

DRS seems fairly more predictive than OAA for now, primarily because it incorporates Catcher data.

And positive defensive data seems more predictive than negative data. Since baseball is a game of failure, taking outs away from your opponents with 100% certainty is more impactful than giving them extra opportunities via errors or misplays – where they still only have about a 33% chance of cashing in.

More MLB Preseason Coverage

• Line Shopping for the best MLB Win Total and Future Prices
• Zerillo: Comparing My Win Total Projections to PECOTA and the Rest of the Market
• Zerillo's Updated MLB Win Totals and Projections

Win Total Outliers

We have shown that, on average, teams who outperform their win total are above average defensively, and teams who underperform are generally below average defensively.

How does this information correlate as a team's performance moves further away from that projected total – whether for good or bad?

I set the outlier boundary at plus or minus 8.5 wins; which ensured that the top and bottom five over and underachievers, in terms of end of the season wins as compared with their preseason listed total, were all captured:

As you can see, teams at the extremes in terms of win total performance trended towards the heights and lows in defensive performance – with the middle two-thirds of the league splitting the difference on a year to year basis.

The data is ever more encouraging when you consider:

• The 3-year average for DRS league-wide is 11; the +8 to -8 teams averaged 9.31
• The 3-year average for OAA is 1.73; the +8 to -8 teams averaged 0.36
• The 2018 sample contains those outlier Diamondbacks (-3 wins), which skews that data

Clearly, there is a strong correlation between defensive quality and teams over or underperforming compared to their win projection.

Over and Under Streaks

With the way that organizations model themselves, it begs the questions of whether individual teams have trended over or under their win totals for consecutive years, and how their defense has performed over that span.

Ten teams (five over, five under) fit the criteria over the past three seasons, and have performed as you would expect defensively, on average:

There are two exceptions in the data.

The Yankees are a bottom-five team by OAA over each of the past three seasons but have utilized their power and bullpen to rack up wins.

Conversely, the Reds are arguably a top-five defensive team over the past three years but have failed to meet expectations thanks to a lackluster offense.

2020 Defensive Projections

Based upon the fielding ratings from the FanGraphs Depth Chart projections, here are the best and worst expected defensive teams, with their 2020 win totals in parentheses, heading into the upcoming season:

Based upon eye test, I would probably kick out the Royals in favor of the Los Angeles Dodgers but otherwise cannot disagree with this preliminary projection.