I was recently thinking about an interesting player in the 1970’s Dave Kingman, nicknamed “Kong”. He hit 442 home runs over a 16-season career, but he was also known for his propensity to strike out. At the time, Kingman was believed a bit extreme in striking out. Times have changed in 2017 where strikeouts are more accepted. Kris Bryant (current slugger) recently made an interesting comment related to power and striking out:
“If you’re able to continue to sustain hitting for power and driving in runs, then nobody cares about the strikeouts.”
This reflects the belief among some players that strikeouts are just a common by-product of a player’s effort to hit home runs.
That raises several questions:
- What is the association between strikeout rates and home run rates? Has the association changed between Kingman’s era (we’ll look at the 1972 season) and the current era?
- Is the strikeout rate and home run rate collectively useful in determining the offensive value of a player?
- Assuming that strikeout rates and home run rates are positively associated, who are some interesting players who buck the trend, that is, combine a high home run rate with a low strikeout rate?
We’ll try to address these questions in this study.
1972 and 2016 Seasons
From Fangraphs I collected the strikeout rates (SO / PA) and home run rates (HR / PA) for all players with at least 250 PA for the 1972 and 2016 seasons. Below I construct a scatterplot of the K Rate (horizontal) against the HR Rate (vertical) for both seasons. This graph shows how strikeouts and home runs have dramatically changed in the 44-year period.
Here are some interesting observations:
- The obvious thing is that the distribution of strikeout rates has drifted substantially to the right between 1972 and 2016. In 1972, many players had strikeout rates under 10% — currently it is unusual to have a strikeout rate under 10%. As we see above, Kingman was really extreme in 1972 with a strikeout rate exceeding 30%. During the 2016 season I count 15 players with a K rate exceeding 30%.
- Also the home run rate distribution has changed a lot in 44 years. There were a number of players in 1972 with no home runs — now it is rare for a player not to hit a home run during the season. In 1972, having a home run rate over .04 was uncommon — now many players have HR rates exceeding .04.
- There is one 1972 player who combined a large HR rate with a low K Rate — Hank Aaron. It is interesting that Aaron had a larger HR rate than Kingman and a much smaller strikeout rate.
- Another interesting observation is that the spread of strikeout rates has increased between 1972 and 2016. Not only are strikeout rates increasing, but there is also more variability in the rates across players.
Discriminating Between High and Low wOBA Players Based on the Two Rates
The weighted on-base percentage wOBA is a good summary measure of offensive performance. How good are strikeout rate and HR rate in understanding the variation in wOBA values? In the scatterplot below, I show a scatterplot of 2016 K and HR rates where I color the point by wOBA — a red point is a player with a “high” wOBA (that is, higher than the median) and a black point is a player with a “low” wOBA. Note that the high wOBAs seem to correspond to players with low K rates and high HR rates.
Suppose we use a logistic model where p is the probability of a high wOBA and we fit the logistic model
log(p / (1 – p)) = constant + a K-Rate + b HR-Rate
We fit this model — the black line represents the values of (K-Rate, HR-Rate) where the probability of a high wOBA is equal to 0.5. The model predicts that players above the line will have high wOBA and players below the line will have low wOBA. How good is this discrimination model? I calculated that this model correctly classified 75% of the players as having high or low wOBA. I label two interesting players who deviate from this black line. David Ortiz is unusual in that he combined a high HR-Rate with a low K-Rate. Travis Jankowski was unusual (in the negative sense) in that he had an unusually low HR-Rate given his high strikeout rate.
- As we know, strikeout rates have been increasing steadily for a while. They continue to increase — the 2016 K rate (K / PA) was 21.1% and today (May 15) the K rate is 21.4%.
- What is the impact of this increase on offensive performance in baseball? An increase in strikeouts may mean a reduction in the number of balls put into play. And with a reduction in the opportunities to put runners on base, I would think we’d eventually see a reduction in run scoring. Or players generally compensating the strikeouts by hitting more home runs?
- Who are the Hank Aarons in modern baseball — the players who hit for high home run rates with small strikeout rates? Generally, I think teams need hitters who don’t strike out. There are situations, say a runner on 3rd with 1 out where it seems important to put the ball in play.