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Chat: Rob Arthur

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Welcome to Baseball Prospectus' Friday June 14, 2019 2:00 PM ET chat session with Rob Arthur.


Rob Arthur is an author at Baseball Prospectus.

Rob Arthur: Hello everyone, happy Friday! Let's get this chat started. Whatcha got?

Al (Chicago, IL): Can you tell us about the Hawk-Eye system? What makes it different from TrackMan? Will it impact the Statcast data we will see next year?

Rob Arthur: Yes, it sure will. I wrote this article about the impending switch to Hawkeye shortly after it was announced: https://www.baseballprospectus.com/news/article/49882/moonshot-baseballs-tracking-data-is-about-to-get-wonky/
To summarize that, it's a camera, not radar-based system; it purports to track more information than the old setup; it's being installed this year and will go live in 2020; and we can probably expect some substantial technical issues when that happens.

rookie319s (Stl MO): How often is DRC+ updated for minor leaguers? Thanks!

Rob Arthur: My understanding is that there were some hiccups early in the season but those should be resolved now and it should be continually updated daily from here on out.

bgawlowski14 (Sea): Hey Rob, Do you have any update on the ball drag from earlier this year? Any difference from April? Thanks!

Rob Arthur: Nope, it's been pretty consistent. There are daily ups and downs but the drag coefficient is still the lowest it's been since 2009 and there hasn't been a material change since the early part of the season. We've seen home runs spike even more with the weather heating up, but that's not drag-related, just the normal progression of the season.

Mike (Albany): You might have written about this but who benefits more from the ball being juiced; big power guys like Judge, medium power guys like Mazara or slap guys like Dyson, who’s already hit his career high in dingers?

Rob Arthur: The ball tends to affect everyone fairly similarly. But to the extent that it is different for different players, it will have the largest impact on batters who hit lots of near-home runs, balls that land at the warning track and such. For these batted balls, the extra few feet the drag coefficient grants turns lazy flyouts into homers. And by and large, it tends to be low-to-medium power players who hit more of these near-homers. When guys like Judge smack the ball, it's usually a no-doubter (if they make solid contact).

mitchellkrall (Cleveland): Is there any chance or evidence that the new, aerodynamic juiced ball is more affected by the advent of warm, summer air than the old ball was?

Rob Arthur: Without doing some physics, my impression is that those two factors act independently. So I don't think so. EDIT: update, I heard from physicist Alan Nathan that a ball with lower drag coefficient would be ever-so-slightly less affected by differences in air density. However, he described the magnitude of the change as effectively imperceptible, considering the difference in drag coefficient we're dealing with here.

boatman44 (Liverpool): Hey Rob,this is a really way out question, but do you know if there is a streaming site for short season baseball(there probably is'nt). But I'm so looking forward to seeing the" four horsemen of the apocalypse" play for Mahoning Valley scrappers against West Virginia tonight,please tell me there is !!

Rob Arthur: Not that I'm aware of, sorry!

Some Guy (Chicagoooooo): Baseball fortunately pairs itself with food. What is your favorite meal experience at a ball park? What could MLB do better with its food? Thanks!

Rob Arthur: Baseball truly does pair well with food. But to be totally honest, I haven't had a lot of great meal experiences at the park. I mean, there's something to be said for chowing down on whatever the greasy ballpark food of the day is, but most of it is gut-busting calorie-bombs, there's not much variety and I've rarely eaten anything that was truly exceptional. I think my favorite ballpark meal is the Cuban sandwich at the White Sox stadium. Baseball pairs even better with beer, arguably, and that's where I tend to devote my attention when I'm at the park.

matthewgtobin (Boston): With launch angle being public, can we come to a consensus on the definition of batted ball types? I was writing about Ketel Marte and noticed Fangraphs has his LD% at 19.7%, Baseball Savant has it at 24.7%, and B-Ref has it at 26%. I imagine that is because the difference between a line drive and fly ball is fuzzy, but with launch angle that shouldn't be a problem.

Rob Arthur: What I've found is that there's solid consensus *within* a system, i.e. FG line drives are like other FG line drives, and B-R's line drives are similar to other B-R line drives, but FG and B-R line drives are different. If you actually break them down by angle, there tends to be surprisingly little overlap in launch angle between the different classes of batted balls. But one system might set the criteria for a flyball around 25 and another at 30, so it's hard to reconcile the two.

There would be value to putting all the systems on the same even footing, but then the companies that sell batted ball classifications wouldn't be able to differentiate their products from each other and that might dampen their sales. So I understand why we have the system we do. The best thing to do is really look at launch angle instead--there is information within a batted ball class that's important. Not all fly balls are created equal, for example.

Kenny (Kansas): Who wins this deal? Yordan Alvarez Carter Kieboom, Peter Alonso, Sixto Sanchez, and Austin Riley for Trevor Bauer and Freddie Freeman?

Rob Arthur: In the near, short, or long-term? Seems like near-term Bauer and Freeman are productive now. At some point it will shift to the other side of the deal. (Don't ask me when. I have no idea.)

Lex (Egypt): Is Lucas Giolito an ace?

Rob Arthur: No. Less than one half of one season of excellent performance doth not an ace make, or something. He's good though, or he has been good, and even if he reverts to replacement performance down the stretch this season will really be something impressive, and a good sign for him going forward.

Rob Arthur: Well folks, it was a pleasure. Now it's time to go outside and enjoy the lovely 70 degree day here in Chicago. Cheers and enjoy your weekends!

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