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Talking Sabermetrics: Astros Trades Walking The Walk

July 30, 2012;Brett Myers was traded to the Chicago White Sox. Mandatory Credit: Jesse Johnson-US PRESSWIRE
July 30, 2012;Brett Myers was traded to the Chicago White Sox. Mandatory Credit: Jesse Johnson-US PRESSWIRE

The importance of the walk---bases on balls---is a well known revelation of sabermetrics. If you look closely at the Astros' recent trade acquisitions, you will see walk rates were an important element of the trade return for both pitchers and hitters. This appears to be a continuation of the Astros' emphasis on walk rates among college players in the recent amateur draft. We will look at analyses which would support the decisions to acquire pitchers with low walk rates and hitters with high walk rates.


Recently acquired minor league hitters whom have above average walk rates are shown below. The applicable league average walk rates are 8% - 9%.

2012 Walk Rate

Carlos Perez 11.2%

Robbie Grossman 14.2%

Marc Krauss 17.0%

We know that walks have significant value at the major league level. But why should major league organizations pursue minor league players with high walk rates? The reason---high walk rates increase the probability of a minor league player's success at the major league level. published a series of studies by Chris St. John which demonstrate that walk rates are the most significant indicators of future success for minor league prospects. A recap of the study is shown here. The Triple A and Double A part of the study are shown here and here.

The review of 400-some Baseball America prospects over a long period showed that both walk and strike out rate have limited value in predicting the success rates of rookie league and low-A hitters. But the predictive value of walk rates grows with each successive level of the minor leagues. At the AA and AAA level, walk rate is noticeably more predictive of major league success than strike out rate. (Indeed, low strike out rates are associated with lower major league success rates at the higher minor league levels.)

The bust rate for high walk rate hitters is 40% and 38% in AA and AAA, respectively, compared to average AA and AAA bust rates of 61% . Moreover, 34% and 42% of AA and AAA high walk rate hitters become productive major leaguers, compared to average AA and AAA percentages of 19-20% .By comparison, 12% of AA and AAA hitters with low walk rates become productive major leaguers. 68% and 71% of AA and AAA hitters with low walk rates become busts.

So, you can see that acquiring high walk rate minor leaguers tends to increase the odds of producing a successful major league player.


Most of the pitchers acquired by the Astros in recent trades have low walk rates. This emphasis on acquiring control oriented pitchers also is consistent with the drafting of control oriented college pitchers in June. The pitchers received in recent trades with good wallk rates relative to their leagues include Rudy Owens, Matthew Heidenreich, Blair Walters, David Rollins, Joseph Musgrove, and Asher Wojciechowski.

Some sabermetric analysts believe that teams often under-value low walk rates in favor of young pitchers with high strike out rates. They contend that baseball teams are more likely to call up young pitchers with good strike out rates but poor control---usually with bad results in the major leagues.

In an earlier article on K/BB ratios for pitchers, I discussed Bill James' findings that avoiding a walk is more valuable to a pitcher than striking out a batter. I will repeat a couple of points from that article:

  • In James' view, avoiding walks is more valuable than striking out batters. His study finds that low strike out-low walk pitchers in general have lower ERAs than high strike out-high walk pitchers. This relationship was more or less consistent across similar pitcher groups.
  • One explanation for the results may be what James terms the "fellow travelers" of walks. Pitchers who give up more walks also throw more wild pitches, hit more batters, and commit more balks. Similarly, James' "high strike out group" (compared to the "low walk group") had 28% more strike outs, which was accompanied by 59% more walks, 70% more wild pitches, 19% more balks, and 19% more hit batsmen.

In that 2011 article, I compared the R-squared for the correlation between Astros' pitchers' ERA and their strike out and walk rates. The R-squared correlation between ERA and walk rate was 36% higher than the correlation between strike out rate and ERA. I repeated the same analysis for 2012 Astros' pitchers, and the R-squared correlation for walk rate and ERA was again 40% higher than for strike out rate.

If indeed pitcher control is undervalued, then my conclusion is that acquiring minor leaguer pitchers who exhibit good control may be a favorable strategy.