The numberless explanation of tRA
I know there are a few people who think tRA is too complicated to understand, what with all those scary numbers in it. Hopefully the following is an easier read than the 'official' primer.
The traditional way of evaluating pitcher effectiveness is ERA. There are a number of glaring flaws with this statistic, the primary one being that you can describe it as follows. 'How many earned runs (unearned vs. earned determined by the subjective home scorekeeper) a team concedes per nine innings when a certain pitcher is on the mound.' If you can't spot a couple of major issues here, stop reading now.
The primary problem, of course, that ERA is much closer to a team run prevention metric than a pitching one. Even at the major league level, defensive ability varies considerably. An adjustment is made for errors, but that's in the hands of a scorekeeper, and you can't make an error if you don't get anywhere near the baseball*. This seems a rather unfair thing to penalize a pitcher for. You see the defense issue popping up all the time - the early 00s Mariners, for example, had one of the best outfields in the history of the game, and their pitchers got all the credit for it. When Mike Cameron was removed from the equation, their ERAs rather predictably collapsed.
A couple of tertiary problems follow:
- Different stadiums have different effects on pitchers and hitters. A pitcher in Arlington suffers immensely compared to a pitcher in Petco Park, even if they are roughly equivalent in talent.
- We shouldn't really care about the unearned vs. earned run distinction, because giving up an unearned run is no different to an earned one in terms of wins and losses.
- ERA tends to fluctuate wildly year to year, which implies that it is divorced from a pitcher's true abilities.
Essentially, we need to look at what a pitcher can actually control to evaluate how good he is at pitching. Seems obvious, right? How?
What we can measure about a pitcher which the defense has no control over:
- Strikeouts swinging
- Strikeouts looking
- Walks
- Hit by pitch
- Ground balls
- Line drives
- Popups
- Fly balls
- Home runs
By only looking at these numbers, defence is more or less entirely eliminated. There are a few robbed home runs every year, but that's neither here nor there. What do we do next? We have to figure out how many runs and outs each of these are worth. This is a long, complicated process, and I'm not going to go into the details here. Suffice to say that every line drive, strikeout, etc over an entire year is examined to see how many runs/outs result, with the average taken after the all of these events have been calculated. And then you can figure out how many runs and outs a pitcher should have given up, without considering his defence, over the course of a year. Much like ERA, tRA is calculated by Runs/Outs*27. Parks are also adjusted for (when measuring the bulleted list above). It's actually a pretty simple concept, and unlike ERA is defence independent, park independent, and much more stable year-to-year (meaning that it's a closer measure of talent - regressing tRA gets you even closer).
There are problems with it, of course - some pitchers' ground balls are hit harder than others', etc, but these issues pale in comparison to the challenges with using ERA to evaluating pitching. Just because ERA is more traditional and fits into the old-school definition of baseball stats better doesn't mean it's right. tRA, as well as other advanced statistics, can be found on StatCorner.
*The Raul Ibanez school of defence.
This post was written by a member of the DRaysBay community and does not necessarily express the views or opinions of DRaysBay staff.
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the link you posted doesnt work. Id actually like to see an example of tRA being used and how the formula works. Im a math minor, so this stuff interests me.
by BossmanJunior333 on Nov 8, 2008 3:40 PM EST reply actions
Quick question
When you say regressing tRA, that would be what tRA* is, right? A more regressed form of tRA, and a marginally better gauge than tRA.
This.
That's how I understand tRA*
I don’t know if it’s a better guage but I think it’s a better indication of future performance.
Brilliant.
How about posting this as a fanshot at BtB and we’ll bump it to the front page over there? I’ve been waiting for a good chance to really pimp tRA and statcorner and this would seem to be it…
Beyond the Boxscore // Calling BJ Upton lazy is lazy.
if we can measure of MPH of the ball off the bat, there would be less discretion (always a good thing) as to what is a line drive and what is a fly ball.
Of course.
Sources say ‘good luck with that’ though. Hit f/x is at the very least several years away.
by Graham MacAree on Nov 9, 2008 3:37 PM EST up reply actions
any idea why that is? it doesn't seem like it should be something that is several years away? I mean, the K-Zone looks a million times complicated than having someone start a gun after contact.
You'd need to laser grid the whole field and that would cost an insane amount of money
by Graham MacAree on Nov 10, 2008 9:50 PM EST up reply actions
Laser grid just owned me in Gears of War 2!
Top Josh Paul Pornos- Big Navi Stroking, 2pitchers1cup, BJ to the Balls, Riggans Your Thingans
09: This one is for all the rings.
We'll trade you bluemax for this guy.
Indie.
by .Taylor on Nov 12, 2008 12:33 PM EST up reply actions
I don't think you guys will like me.
Top Josh Paul Pornos- Big Navi Stroking, 2pitchers1cup, BJ to the Balls, Riggans Your Thingans
09: This one is for all the rings.
Do you post motivators all the time? And not use punctuation?
If so, probably not.
We’ll take Sky Kalkman for Coach, tho.
Indie.
by .Taylor on Nov 17, 2008 1:15 AM EST up reply actions
Laser grids have become surprisingly less expensive in the last few years
I think they just need to run a Large Hardon Collider around the perimeter of the field and see what happens.
Anyway, as I was lying in the puddle, I think I may have found
a way for us to get Bonds and Griffey, and we wouldn't have to give up
that much.
~George Costanza~
by Sandy Kazmir on Nov 11, 2008 10:54 AM EST up reply actions
Rec'd because Graham puts up with my shenanigans. :)
Indie.
by .Taylor on Nov 9, 2008 4:06 PM EST reply actions






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