There is considerable teeth-gnashing going on around the game due to a lack of action on the field. Those criticisms are not unfounded. All things being equal, the game is better with more and not less action. A walk might be nearly as good as a hit when it comes to scoring runs, but it is considerably less exciting. A strikeout does have some excitement of its own, but on a large field that ranges out to 400 feet in most parks, concentrating much of the action to the first 60 feet has some drawbacks when it comes to demanding and retaining the attention of fans.
In any given confrontation, both the pitcher and batter exert considerable influence over the outcome of an at-bat. Because of that, it might seem reasonable to place equal blame on the hitters and pitchers for the increase in strikeouts. In an era defined by greater velocity and more frequent shifts, one argument goes, batters are failing to adjust. If they would just take the ball the other way, they might strike out less, get more hits, etc.
That might be true. It is also possible, however, that changing their approaches might lead hitters to produce less valuable outcomes or, worse, abandon the very strengths that allowed them to become major leaguers in the first place. That isn’t fair to hitters. What I’d like to posit here is a much simpler explanation for the rise in strikeouts — namely, that pitchers are too good.
Fastball velocity has increased at a steady rate, some of that due to the rise of relief innings around the league and some of it probably to dramatic improvements in training and development. That’s not really the point of this post, though. The point of this post is to discuss one particular cause of the increase in strikeouts that likely has little to do with launch angle or players trying to hit home runs, but rather the talent level of the pitchers and a change in philosophy.
Below is a scatter plot of MLB strikeout percentage and average fastball velocity.
As you can see, the two are highly correlated. That’s something we probably already knew. Over the same time period, I compared a whole host of other stats — mostly rate stats, as well as plate-discipline numbers — to see if I could find other numbers that moved in the same, or opposite, direction of strikeouts over the last decade and a half. The most similar was the increased use of offspeed pitches, as seen below.
At the same time we have witnessed a rise in fastball velocity, we have also witnessed a decline in fastball usage. No other metrics reveal such a strong relationship. I suspected that walk rate might have moved with or against strikeouts, but that hasn’t really been the case. I thought that if hitters had been selling out for power, we might see a correlation with ISO, but that’s not really true, either. When I ran the strikeout numbers against the plate-discipline numbers, there were several really good relationships. One such relationship was first-strike percentage, though perhaps that is a bit too obvious, as getting strike one is clearly going to increase the odds of a strikeout.
As for the other plate-discipline numbers, the closest relationship occurred on zone percentage, perhaps in the opposite direction we might expect.
Pitchers have steadily worked in the zone less often over the years, even as strikeout rate has moved up. In order for that to happen, players would have needed to swing on a lot more pitches outside the zone… which they have. Graph:
What’s interesting here is that O-Swing% has been fairly steady over the last seven years even while strikeouts have continued to climb. It’s possible to place some blame on the batters for increasingly swinging at pitches outside the strike zone, but contact on pitches outside the zone actually went up with O-Swing percentage a decade ago, and it wasn’t until after the swing rate hit a plateau that contact rate moved down over the last few seasons. The 62.5% contact rate on pitches outside the zone this year is actually higher than for any season between 2002 to 09.
To put these changes in more concrete terms, let’s take the numbers from 2013, where hitters swung at 30.3% of pitches outside the zone and made contact 66.5% of the time. Knowing only that pitchers were pitching in the zone one percentage point less often, we would expect a change in whiff rate by 0.1 percentage points. When we factor in the drop-off of contact on those pitches from 66.5% to 62.5%, the number of whiffs due to pitches swung at outside the zone changes things just .11 percentage points. That’s not a whole lot when whiff rates have moved up 1.2 percentage points during that time.
If the change in whiff rate over the last five years isn’t due to hitters chasing pitches outside the zone, then what is the cause of the climb in whiffs and strikeouts?
Let’s attempt to answer that by revisiting a couple of the earlier graphs above. The two strongest relationships with strikeout rate have been fastball velocity and percentage of offspeed pitches. Let’s see how those changes from 2013 to 2018 might have had a tangible effect on whiff rates.
The table below puts fastballs into buckets by velocity and the compares outcomes in 2013 and this season, per a number of searches over at Baseball Savant.
|Velo||2013 Pitch%||2013 SwStk%||2013 wOBA||2018 Pitch%||2018 SwStk%||2018 wOBA|
Given the roughly equivalent offensive numbers by wOBA in roughly similar offensive environments, players seem to have adjusted pretty well to velocity over the past five years — or, alternatively, have been aided by a juiced ball. While the whiff rates have gone up in the 95-97 mph range, the overall outcomes are the same. It is at the lower velocities where hitter numbers have declined the most. Those numbers are relative as hitters still hit better against lower velocity than upper velocity.
What is interesting is that if you ignore the whiff numbers in 2018 and looked at only the whiff rates in 2013 as well as the change in frequency of pitches at 95 mph and above, you would expect a change of about .14 percentage points in whiff rate, which is more than the change on hitters chasing pitches out of the zone.
Let’s do another similar analysis with offspeed pitches, just looking at whiff rates.
|Season||Pitch %||Whiff %||wOBA|
So we see, again, that hitters have adjusted (or been aided by a juiced ball) to the increased use of offspeed and breaking pitches, putting up similar offensive performances in the 2013 and -18 seasons. The big problem for hitters is that breaking pitches have always induced more whiffs. If we only use the whiff percentage from back in 2013 and the increased usage over that time, we would see a rise of .24 percentage points, an even bigger rise than the one from more 95-plus mph fastballs. Those two factors together account for one-third of the rise in whiff rate over the last five years without even accounting for the rising whiff rates on fastballs and non-fastballs.
Without factoring in pitcher command, harder breaking balls, chase rates, or increased emphasis on power, we find that a large amount of the rise in whiff rates — and ultimately in strikeout rates — is due to two factors:
- More pitches 95+ mph; and
- More offspeed and breaking pitches
There are certainly a lot of other variables in play, but before blaming the hitters for changing their approach, keep in mind that much of the rise in strikeouts is due to factors out of their control. While hitters have been forced to adapt/take advantage of the juiced ball and potentially avoid shifts by hitting over them, a good portion of this rise in strikeouts was inevitable due to increasingly more talented pitching.
Craig Edwards can be found on twitter @craigjedwards.