Hitter Aging Based on Ability to Hit Different Pitch Types

This study came about from a comment made in passing by Jeff Erikson and Scott Jenstad in a RotoWire podcast. They were discussing how they were worried more about hitters who were striking out on fastballs instead of breaking balls. They figured it was worse to strikeout on fastballs and it showed the hitter was in decline. I don’t remember the exact show but I agreed and now have time verify. And as usual, the pair was right with three-hitter groups differentiating themselves from the pack.

The first key was that I wasn’t interested in the batter ability to tell balls from strikes. Instead, I wanted to focus on pitches right down the heart of the plate while keeping the strike zone as big as possible to increase the sample size. In the end, the taken pitches in the zone used were called strikes 97% of the time.

Next, I found the swinging strike rate for pitches in the strike zone. I grouped the pitches into several groups.

• All fastballs
• Fastballs > 94 mph
• Fastball < 94 mph
• All non-fastball
• All changeups including splitters
• All breaking balls

My first step was to find if the values had any year-to-year correlation. Once the sample got to 10 pitches in the heart, the r-squared stabilized at .40 (R of .63). I was surprised it was so high but most plate discipline number stabilize quickly.

From there, I just started cutting-and-dicing the numbers up. To find possible areas of focus, I compared the hitter’s projections versus results. In the end, three benchmarks stood out which pointed to hitters performing better or worse than their OPS projections.

• Slow fastballs: > 15% SwStr%
• Changeups: > 30% SwStr%
• All breaking balls: < 5% SwStr%

Let me go over each group in detail with all hitters listed here and all the standard, non-heart, pitch type metrics are available on the player pages.

Slow fastballs

This finding is not really a surprise that batters who can’t hitter slower fastballs can’t cut it in the majors. On average, these hitters underperform their adjusted projections by 15 points of OPS. A 15% SwStr% is high against breaking balls tyet alone against fastballs.

This difference leaked over to the all-fastball results but the faster fastballs showed no divergence. To show how this difference adds up, here is the group’s OPS aging curve and the rest of the hitters.

What a career nose dive by these hitters. And the hitters to worry about next season are:

Only two names stick out, Ian Happ and Scott Schebler. The pair can’t cut it in the majors if they can’t hit fastballs and were thought to have some fantasy upside. In NFBC events, they are going at pick 250 and 269. I’d rather gamble on someone else.

Changeups

Weirdly, the numbers work out that once hitters miss on 30% of changeups right now the middle, their average adjusted OPS is 16 points lower than expected. So, if a hitter can’t hit a slow pitch right down the middle, they are going to have a rough time. Wow!

Their aging curve is not as steep as the slow fastball one but these hitters do age faster than the rest of the league.

The key here is that there curve doesn’t have any up or level aging sections. It’s just all downward. And how about those who struggled last season who could under perform their projections. Here they are.

One big name sticks out, Aaron Judge. Changes just own him. He’s nearly elite with fastballs but changes eat him up Cerrano style.

Non-Fastballs

Of the groups who aged better, this grouping was the best but the difference is barely noticeable. These players are only able to beat projections by an average of 4 points of OPS. And this grouping was the best instance of beating the projections. Projections are based on the players, who can hit a baseball, staying in the league. They are going to be based on the rule, not the exception.

As for the aging curve, it takes years before a difference materializes.

Finally, here are the batters from last season who fit into this group.

Not surprisingly, some of the league’s best hitters (e.g. Trout and Betts) are in this group. I’m more interested in some of the lesser names like Jose Peraza, Danny Jansen, and Rowdy Tellez and how they’ll perform going forward.

In conclusion, the main group I’d focus on as fantasy owners are those who can’t hit slower fastballs. Discount them. They are going to see heaters 50% of the time and need to make contact. These players just don’t stay in the league long and age horribly. Also, those who can’t hit changeups struggle to meet their projections. The one group who barely beats their projections are those who don’t miss on breaking balls in the zone. In all fairness, I expected to find nothing. I suspected the bad plate discipline would show up in the projections but that was not the case. Instead, I got a list of hitters to avoid at their current price and others to feel good about.