Pitching When One is Facing a Rookie

I’m not gonna lie to you — I’d love to be writing about something more compelling. Perhaps some unexplored Clayton Kershaw angle, or perhaps something else entirely. At the end of the day, traffic does have to be there, and traffic follows entertaining, easily-understandable blog posts. It doesn’t so much follow posts about what it’s like, statistically, to pitch to a rookie in Major League Baseball. But we’re all just slaves to the ideas that we have at any given moment, and after I messed around earlier with league-wide leaderboards, I felt the urge to keep messing around in the same place. I promise this is just a phase.

Earlier I did what I could to investigate whether or not veteran pitchers and veteran hitters get the benefit of the doubt from home-plate umpires when it comes to the called strike zone. Those are theories I’ve heard repeated time and time again, and they were easy enough to look into. That got me thinking about other well-worn baseball theories, and I wound up growing curious about how big leaguers have approached rookies, relative to how they’ve approached non-rookies. Do rookies get fed a steady stream of breaking balls? Alternatively, do they get fed a bunch of fastballs in the zone? Is there any meaningful difference in how rookies are pitched to? It didn’t take a lot to put some numbers together.

The FanGraphs leaderboards make things easy because they have a “Rookie” check box which you can toggle or un-toggle. And we’ve got all the necessary league-wide statistics, where, in this case, we’ll be going back to 2002, since that’s where we find our oldest pitch-type data. There’s nowhere to look up the performance of non-rookies, but that’s all easy enough to calculate given rookie performances and given overall performances.

I’ve heard it suggested sometimes that rookies have to prove early on that they can hit slower stuff. I’ve also heard it suggested sometimes that rookies have to prove early on that they can hit hard, challenging stuff. Intuitively, they both can make sense. With regard to the former, rookies usually haven’t seen many big-league-caliber offspeed pitches. With regard to the latter, they also usually haven’t seen many big-league-caliber fastballs, and pitchers like to keep with their fastballs unless they have to throw something else. So a theory is that rookies have to earn the other pitches.

We’ll have to settle for what information we have. Now, two tables. The first spans the majors between 2002 and 2013, excluding pitchers. The second spans the majors between 2008 and 2013, excluding pitchers, covering the PITCHf/x era. Pitch-type data comes from Baseball Info Solutions. Here are the overall pictures:

2002-2013 FB% SL% CB% CH% F-Strike% BB% K% wRC+
Rookies 60.5% 14.3% 9.6% 10.5% 60.1% 7.5% 19.8% 87
Non-rookies 60.2% 14.4% 9.3% 10.8% 58.4% 8.8% 16.8% 102
Difference 0.3% 0.0% 0.2% -0.3% 1.7% -1.2% 2.9% -15

2008-2013 FB% SL% CB% CH% O-Swing% Z-Swing% Zone% F-Strike% BB% K% wRC+
Rookies 58.8% 14.8% 9.6% 10.2% 29.6% 62.1% 50.3% 60.3% 7.6% 20.5% 87
Non-rookies 58.3% 14.9% 9.3% 10.4% 28.4% 62.3% 49.7% 58.7% 8.7% 17.8% 102
Difference 0.5% -0.2% 0.2% -0.2% 1.2% -0.2% 0.5% 1.6% -1.0% 2.7% -15

You’ll notice how close everything is. Everything until you get toward the end of the tables. Rookies have consistently drawn fewer walks, and racked up more strikeouts. They’ve produced at a considerably lower level than non-rookies, with a wRC+ that’s worse by about 15 points. That all makes pretty good sense — rookies have to adjust to the toughest level anywhere, and non-rookies are selective for guys who’ve already had some big-league success. Way to go, non-rookies!

Turn back, now, to the stuff we’re trying to investigate. Over the years, rookies have been thrown more fastballs, very slightly. They’ve been thrown more pitches in the strike zone, very slightly. They’ve been thrown more first-pitch strikes, less slightly but still slightly. It would appear that there’s a small effect, but that rookies have been challenged a little more, relatively speaking.

But, about that last column. Because there are differences in the last column, we should expect there to be differences in some other columns. There’s a fairly strong relationship between wRC+ and fastball rate. There’s a stronger relationship between wRC+ and zone rate, and between wRC+ and first-pitch-strike rate. All of those numbers have at least something to do with the quality of the hitter, and it would appear that rookie hitters are of a lower quality.

It’s hard to establish directionality, here, but just based on the wRC+ difference, we’d expect rookies to have a higher fastball rate by 1.1 percentage points. We’d expect them to have a higher zone rate by 1.0 percentage points, and we’d expect them to have a higher first-pitch-strike rate by 1.1 percentage points. What we observe is that the difference in fastball rate is smaller. The difference in zone rate is smaller. The difference in first-pitch-strike rate is a little bigger.

So that makes it look like rookies have been challenged slightly less often. But what I imagine is going on is that rookies have fallen behind unusually often, ending up in more breaking-ball counts. That is, they’ve fallen behind more than the average 87 wRC+ hitter. Only by a little, but we’re only dealing with a little.

The end result being that it doesn’t look like there’s much of a difference anywhere here outside of the production. Rookies haven’t been fed an unusually steady diet of anything. They’ve been pitched like big-leaguers, big-leaguers who swing below-average bats. Some rookies get more fastballs and some rookies get more breaking balls, but the same goes for non-rookies as well, and it just has to do with one’s perceived batting profile. That becomes known pretty quick, if it isn’t already known when a guy is fresh out of the minors. Teams are constantly scouting, everywhere.

If I had access to better numbers, I’d break this down. A full rookie season lasts a long time, and by the end, the player is hardly a rookie anymore. It would be of particular interest to look at the same data covering just a player’s first, say, month in the major leagues. Toward the beginning is when you’d expect any effect to be at its greatest. As more times passes, you expect things to even out. But if there were a huge initial difference, you’d think that would still show up in the full-year differences, and there’s just not much. Rookies seem to get pitched more or less as they ought to.



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Jeff made Lookout Landing a thing, but he does not still write there about the Mariners. He does write here, sometimes about the Mariners, but usually not.


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gnomez
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gnomez
2 years 5 months ago

I wonder if the sample size provided just by the checkbox “rookie” is too large. Over the course of a season, teams likely have enough material from their scouts to know even a rookie’s weaknesses. It would be a lot more work to parse, but I’d be interested to see a data set over just, say, a hitter’s first week, or first 30 plate appearances, before, as announcers say, they have a “book” on the player.

Expanding from that idea, I wonder if the conventional wisdom about the pitches rookies see was true at one time, in a time when scouting reports of minor leaguers may have been less detailed or less available throughout organizations.

tz
Guest
tz
2 years 5 months ago

On a related tangent, does anyone have any idea if anyone provides splits based upon first time facing a pitcher vs. 2nd, 3rd, 4th time etc.? And similarly for pitchers’ 1st, 2nd, etc. time facing a particular batter.

I’m curious whether certain players do better the more they see a particular “opponent”. Scouting report detail has probably eliminated a lot of the mystery behind players strengths and weaknesses, but there may be a way to quantify the skill set of how well someone “works” the opposing pitcher/hitter plate appearance by plate appearance.

Steve the Sage
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Steve the Sage
2 years 5 months ago

Survivor bias.

DrFarmer
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DrFarmer
2 years 5 months ago

Shouldn’t these numbers be adjusted for annual league averages? Reminds me of some of the misgivings with the recent aging curve posts.

brypot
Member
brypot
2 years 5 months ago

Thank you Jeff.
I agree the first month would be interesting.
Last year Nick Franklin got a load of Fastballs until he started barrelling them out on a regular basis, then he got all the breaking balls whereupon he starting swinging like a rusty gate.

@outfieldgrass24
Guest
2 years 5 months ago

See: Gregorius, Didi

Dave S
Guest
Dave S
2 years 5 months ago

Also: Brown, Domonic (though not technically a rookie)

B N
Guest
B N
2 years 5 months ago

Anecdotally, this does seem to happen. I do think that with the improved scouting of modern baseball, it happens a bit less and corrects itself quicker.

I remember seeing pitchers on certain teams consistently throw heat to rookies, despite the fact that some rookies were KNOWN (by anyone watching any level of games or with access to their minors stats) to be good with fastballs and completely unable to lay off anything in the dirt. I haven’t seen that happen as much lately, at least.

HaileeDunphyvin
Member
HaileeDunphyvin
2 years 5 months ago

My Uncle Bentley just got an almost new blue BMW M4 Coupe by working parttime from a home pc. you can try this out……. iop.li/8wv

Ghost of Brien Taylor
Guest
Ghost of Brien Taylor
2 years 5 months ago

Wow, “almost new?” I’d be skeptical if you’d said “completely new”, but as it is, I’d sure love to meet your Uncle Bentley! Please have him call me at 1-800-fuc-koff so we can talk!

I shall anxiously await the response of your most appreciated numerals!

B N
Guest
B N
2 years 5 months ago

Indeed! Get Bentley immediately!

Trolly McGee
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Trolly McGee
2 years 5 months ago

More interesting story than the article

baycommuter
Member
baycommuter
2 years 5 months ago

Funny, my uncle Beemer just got an almost new Bentley, working for organized crime part-time out of his black sedan.

witesoxfan
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witesoxfan
2 years 5 months ago

I think you mean running a car wash.

DerekJeterGiftBasket
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DerekJeterGiftBasket
2 years 5 months ago

When I was a kid, I went with my uncle to buy a used car. As he drives off the lot, with me in the front seat, he rips a gigantic fart and says “There. Now it’s mine!”

The Humber Games
Guest
The Humber Games
2 years 5 months ago

Tell me more, oh poster whose name sounds like an obscure single malt scotch

HollywoodMcMoon
Member
HollywoodMcMoon
2 years 5 months ago

Jeff,

Some of the things I would like to know are:

1. Are there material changes in approach to rookie hitters once they have accumulated a certain amount of PA or if they have achieved a baseline of solid results after X number of plate appearances?

2. Not that it is perfect, but is there a difference in approach to these rookies which somehow correlates to their minor league ISO. I’d be more likely to attack a minor league power hitter with breaking pitches out of the gate and I’d be far less likely to throw first pitch strikes or fastballs in order to try and exploit any aggressive tendencies. Generally, with a low ISO/high contact guy, I’d tend to want to try and knock the bat out of his hands.

3. Is there a difference in approach to rookies which occurs based upon their position (based upon the idea that a middle infielder is more likely to have a profoundly different set of hitting skills than a corner outfielder or corner infielder)?

tdi1985
Member
tdi1985
2 years 5 months ago

Forgive me if this has been done before, but have we regressed pitch types on wRC+? The way the data is put together here, it seems like a leap of faith to assume any modest changes in pitch type weightings explain any variation in wRC+ from Rookies and Non-Rookies.

The Humber Games
Guest
The Humber Games
2 years 5 months ago

I wonder if you could restrict this to first plate appearances. It wouldn’t make sense to challenge a rookie all season, as at some point they’ve started making adjustments and getting acclimated, and at some point they’ve proven if they can hit a decent big league pitch. Just from watching games it does *feel* like rookies get more ‘try and hit this!’ fastballs in their first plate appearances, but that could just be confirmation bias talking as that’s the accepted narrative.

The Humber Games
Guest
The Humber Games
2 years 5 months ago

Hmm, I shouldn’t have skipped the last paragraph ;)

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