Can Walk and Strikeout Percentages Be Used to Evaluate Performance?

After reading fellow contributor John Stolnis’ analysis of baseball’s most out-prone hitters, it got me thinking about other trends in baseball -- specifically walk percentage (BB%) and strikeout percentage (K%).

Like most stats, BB% and K% are not perfect indicators of a hitter’s performance, but they can help paint an overall picture of a hitter’s ability. What I found is not breaking news, but rather confirms what is already widely known within baseball.

What can walk and strikeout percentages really tell us about a hitter? And can they be applied to fantasy baseball, as well?

The Process

There were 146 qualified hitters last season based on number of plate appearances, and I looked at BB% and K% for each hitter.

I then examined the BB% and K% of the top-50 hitters. In order to determine what a “good” hitter is, I used Weighted On-Base Average (wOBA) and Weighted Runs Created Plus (wRC+). Both stats attempt to measure a player’s offensive value, which is why I chose not to use Wins Above Replacement (WAR), since that is a reflection of a player’s overall value, which includes his defense.

I chose to group players into three tiers (above average, average, and below average) based on their wOBA and with their wRC+. I followed FanGraphs’ general guideline when analyzing wOBA, which is that an above-average hitter’s wOBA would be .340 or better, an average hitter’s is .320 to .339, and a below average hitter’s is .310 or worse. Of course, this is a general guideline, so these marks change from season to season.

Conversely, we don’t have this concern with wRC+ because league average is always considered 100.

I then compiled hitters into groups of 50 based on their BB% and their K%. For example, the hitters that make up the category “High BB%” are simply the top-50 hitters ranked by BB%, while the hitters that make up “Low BB%” are the bottom-50 hitters ranked by BB%. I did the same for K%.

The Results

Here’s what I found based on the top-50 of the 146 qualified hitters.

These tables display the amount of hitters (among the top 50) who landed above, at, or below the cutoffs for wOBA and wRC+. In parentheses are the percentages of the 50 player subset that met the given criteria.

The Analysis

The overall totals and percentages are roughly the same for wOBA and wRC+, with slightly more hitters falling in the “above average” category for wRC+.

Based on both metrics, hitters with a high BB% tend to be above-average hitters, while having a low BB% generally means the opposite. The totals for K% show that this statistic largely plays no role in determining the offensive value of a hitter, as the odds of being either an “above-average” hitter versus a “below-average” hitter are roughly the same.

The idea that batters with a high strikeout rate are “bad” hitters is false, as is the idea that batters with a low K% are “good” hitters based on wOBA and wRC+.

As always, there are exceptions to these “rules.” For example, Adam Dunn had the fifth highest BB% last season at 13.9% yet managed a wOBA of .334 and a wRC+ of 112, both good for 64th best -- and both considered “average.”

Conversely, Adam Jones had the second lowest BB% at just 2.8% last season, but both his wOBA (.340) and his wRC+ (117) are considered “above-average” totals.

Again, none of this information is necessarily groundbreaking, but it can be used to your advantage when targeting fantasy players in your drafts. You can use a high BB% as a tie-breaker between two players you are close on while mostly avoiding those with a low BB%, but don’t let a high K% scare you away from selecting a hitter you otherwise would.