Baseball Defense

Key Metrics For Baseball Betting


With the 2022 MLB season getting underway, TheLines has prepped some primers on key metrics that can aid your daily handicapping. Thus far, we’ve tackled a variety of pitching metrics and have taken a look at the best way to evaluate baseball offense. For the final entry in this series – at least for now – we’ll look at baseball defense.

So, how can we evaluate baseball defense and how can you apply it to betting on baseball?

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What Is Baseball Defense?

This article will take a bit of a different track than the others because baseball defense has proven difficult to quantify. An elusive “dominant” defensive metric has not yet emerged even after considerable research into the subject.

Essentially, we want to know which defenses will do the best job converting outs for their pitchers. This will keep opposing offenses in check and elevate the team’s win probability.

The problem comes in the question of how we evaluate defense. Again, there’s no clear-cut best method. The best way is going to involve cross-checking between a variety of metrics. Among the useful ones, which we’ll discuss here: outs above average (OAA), ultimate zone rating (UZR), defensive runs saved (DRS) and defensive efficiency (DefEff).

Finally, we should also factor in catcher defense, particularly framing ability.

More key baseball metrics

Why Is Baseball Defense Useful?

While the talent level of the starting pitcher (and, to a lesser extent, the bullpen) is the most important factor in determining a team’s run prevention, defense also plays a large role. Critically, the biggest turning point defensive plays can turn extra base hits into outs and stop multiple-run rallies to end innings. Likewise, missed plays can turn outs into extra bases. These plays can cause massive swings.

Knowing which teams have elite defenses will help you figure out which pitchers will outperform their own talent levels and which pitchers will likely underperform. That is to say, it may not always be a fluke when certain pitchers have better (or worse) ERAs than their estimators would seem to indicate they should.

Using Baseball Defense: How Adam Wainwright Enjoyed A Throwback 2021

One-time Cardinals superstar pitcher Adam Wainwright put together a banner 2020 season with a 3.15 ERA and 1 fWAR in a mere 10 starts.

Obviously, the sample was small. Given that he was coming off three straight seasons of around a 4.5 ERA before that and his 2020 ERA estimators also sat around those same numbers, there was every reason to expect him to regress very heavily in 2021.

Wainwright proved doubters wrong, however, by actually improving in 2021. He posted an even better 3.05 ERA with the best ERA estimators he had since 2014. Yet, most of Wainwright’s peripherals were not out of line with previous seasons. His fastball velocity remained poor at 89.3 mph. His swinging strike rate was still a well below-average 8.1%. The only thing that sticks out at all is a .256 BABIP (batting average on balls in play) almost 40 points below his career number.

So, what happened? Well, the Cardinals trotted out one of the best defenses in MLB, which likely contributed heavily to said BABIP. They ranked second in DefEff, first in OAA, fifth in UZR/150 and second in DRS. Basically, pick your defensive metrics of choice, and the Cardinals defense rocked.

They lagged only in catcher framing, with Statcast’s leaderboard not a fan of Yadier Molina’s work there.

Use Defense To Help Evaluate Team Run Prevention

The key concept here is that simply using Adam Wainwright’s talent level to estimate the team’s run prevention isn’t going to work when he has an elite defense behind him. With a below-average strikeout rate, he relies heavily on balls in play being turned into outs. Luckily for him, the Cardinals excelled in that department.

If you only handicap the Cardinals’ run prevention based on Wainwright’s ability, you’re going to be low on the Cardinals’ price every day that he starts, and likely every other day as well. You have to adjust the Cardinals pitching upward a little bit because guys like Nolan Arenado, Harrison Bader and Tyler O’Neill provide good-to-elite glove work behind them.

An important concept to remember is this is especially true of guys like Wainwright who allow a disproportionate amount of batted balls.

Again, always use multiple metrics to cross-check defensive ability. Sometimes they disagree significantly, especially on individual players.

Catcher framing is important as well and a separate animal entirely. As best I can tell, metrics like DRS and UZR do not account for it, so you’ll need to dive into that separately. Statcast has a leaderboard linked above, and I believe FanGraphs team defense page has a framing metric listed under the “Advanced” tab under the column “FRM.”