Why do the Rockies under perform actual HRs vs expected HRs?

[whalewang]

Ref: https://baseballsavant.mlb.com/leade...e=Batter&min=0

Pretty sure it's park related but I don't understand why the Rockies hitters don't hit as many HR as they are expected to. Can someone explain why?

[rhd]

Ref: https://baseballsavant.mlb.com/leade...e=Batter&min=0

Pretty sure it's park related but I don't understand why the Rockies hitters don't hit as many HR as they are expected to. Can someone explain why?

Coors Field has some of the deepest fences in the league. This was to offset the fact that balls travel farther in the this air. Despite this, the HR park factor at Coors was still above average for 2021 (1.134). So one would think that the actual HR rate actually would be higher than the expected rate. So I dont know. It would help if I knew how Baseball Savant is figuring the expected HR rate. I couldnt figure it out by looking at the stats on that chart. All it says for this is "Ballparks gone out at divided by 30". And for "Mostly Out" it says 8-29 parks and for "Doubters" 1-7 parks but it doesnt provide any figures for estimated likelihood that a particular fly ball would go out in an "average" park.

[Todd Zola]

I know the answer, but am not home and is too much to type on phone, more later.

[rhd]

I know the answer, but am not home and is too much to type on phone, more later.

Thanx. Looking forward to your answer. Whatever the answer, I think Baseball Savant could do a much better job of explaining how they figure their xHR value.

[Todd Zola]

So here's the deal. Statcast takes the flyball distance and essentially overlays it onto all 30 parks (I don't know how they handled Dunedin/Buffalo/Toronto, nor stuff like the Field of Dreams game, but it doesn't matter for this explanation). They determine the number of venues the flyball distance would have been a homer. Say it was far enough to be gone in 15 parks. It has an xHR of .5 (15/30). This is what they mean by xHR: Ballparks Gone At/30 (on the Statcast page).

With Rockies, it's not about the homers, but the flyballs going far enough to be out of most parks, but not Coors. A 425 foot flyball could be a double, or even an out at Coors, but would be gone just about everywhere else. Say it was a homer in 27 parks. It gets credited as .9 xHR, but it was off the wall in Coors.

Just about every homer in Coors is 1.0 xHR, since it was far enough to be gone everywhere (30/30).

Trevor Story hits a ton of fly balls, career average 45%. He's going to launch several that are far enough to be souvenirs almost everywhere else, but are 2B, 3B or outs at Coors.

These go on his ledger, so his xHR reflects all these non-HR.

The part bugging me most is this isn't even a "Statcast" thing, other than measuring the flyball distance.

I talk about this a lot on Podcasts and SXM, and have written about it. Too many use the expected stats from Statcast without understanding their emanation, hence end up misapplying them. The Internet is flooded with pieces listing "lucky" and "unlucky" based on xWOBA, or xSLG or xBA or xBABIP, without having a true grasp how the xStats are computed.

[whalewang]

Thanks Todd and rhd.

[rhd]

So here's the deal. Statcast takes the flyball distance and essentially overlays it onto all 30 parks (I don't know how they handled Dunedin/Buffalo/Toronto, nor stuff like the Field of Dreams game, but it doesn't matter for this explanation). They determine the number of venues the flyball distance would have been a homer. Say it was far enough to be gone in 15 parks. It has an xHR of .5 (15/30). This is what they mean by xHR: Ballparks Gone At/30 (on the Statcast page).

Thanx, Todd. So really there is no way one can look at the data provided on the page at the link above and figure the xHR yourself because they dont indicate how many parks the fly balls would have been HRs in because it tells you only that it would have been out in 8 to 29 parks or in 1 to 7 parks. You just have to use the xHR figure displayed that they calculated themselves behind the scenes.

And so the HR Park Factor apparently has no correlation w xHR because it's measuring something completely different.

[Todd Zola]

Thanx, Todd. So really there is no way one can look at the data provided on the page at the link above and figure the xHR yourself because they dont indicate how many parks the fly balls would have been HRs in because it tells you only that it would have been out in 8 to 29 parks or in 1 to 7 parks. You just have to use the xHR figure displayed that they calculated themselves behind the scenes.

And so the HR Park Factor apparently has no correlation w xHR because it's measuring something completely different.

Yeah, the correlation gets busted because there's so many different factors feeding into how a venue plays. Temperature, humidity, altitude, batter's eye, wind, dimensions, fence height etc.