In any case I want to apologize for attacking you personally. That was inappropriate. If there is anything I can do for you now or in the future, such as helping you with any research, let me know and I’d be happy to assist.

Tango’s post does not prove what you say.

(1) I find it ironic that you call me out for failing to use facts, and then misquote the very article you cite. Tango corrects the method to adjust his sampling:

“Note that the rate column for year 1 is marked as “regressed” to avoid confusion. Now, the CHAIN column looks much more reasonable: The peak is from ages 24 to 28, and then the drop is only five plays per year. In the three years leading up to age 24, the gain averages eight plays per year.
The degree of regression will establish the peak age and the slope toward the peak age. I tried different regession values, and it always maxes out at age 28. So, that is one conclusion we can make: On average, shortstop fielding prowess peaks no later than age 28. Recall that, in the first (unregressed) table, the peak age was around 23. So, the true answer lies somewhere between these points (without regression and with maximum regression). The second chart above seems to satisfy this condition.
As for the slope toward the peak, that’s another issue. I can adjust the regression so that we have very little slope (only one fewer out per year), whereas with no regression, the slope was nine outs per year. What is the real answer? I don’t know yet. But, my guess is that the second chart above will likely be very close to the final best answer.”

It looks like a median age of 27 for elite FRAA would be exactly in line with Tango’s findings that shortstop fielding value maxes out at age-28.

(2) I am not a journalist. I am a fan writer. I don’t have any ethical responsibilities. I am writing for fun whenever I have time, and I’m not getting paid to do so. If you believe this is irresponsible, I kindly ask you to read other sources.

OK

http://www.hardballtimes.com/fielding-aging-curves/

“What this chart shows is that there’s a defensive peak for shortstops from ages 22 to 24, and then a long progression downward as the shortstop ages.”

Median (or mean) age for percentiles don’t tell you peak age for anything. There are different players at different ages. The only ones that survive at SS at age 27 or 28 are the best ones, defensively.

In order to estimate peak age or aging curves for anything, you must use matched pairs otherwise known as the delta method. Before you write articles like this I suggest you familiarize yourself with this concept. Tango, me and others have been writing about it since you were probably in diapers.

So, no, I am not wrong. I’ve been doing aging curves and defensive analysis probably since before you were born.

UZR/150 and DRS don’t like Arcia right now. Inside Edge loves him, and so does FRAA. So, pick your poison, I guess. If you love zone stats, then Arcia looks bad. DRS, he’s a wash. FRAA and Inside Edge, he looks strong. Draw from that what you like.

Mostly, though, have you looked at UZR and DRS? Both have him minus in 2016 and around zero in 2017. Now, I’m not saying that FRAA is “wrong” or a “bad metric,” but if you combine FRAA with DRS and UZR, you are not going to conclude that Arcia is an “elite fielder.”