What is tRA?

As I’m sure many of you have noticed, tRA has come to FanGraphs. I’m going to try to describe it as concisely as possible, so here goes.

tRA can be seen as an extension of FIP including batted ball types, namely line drives, ground balls, and the different types of flyballs. The idea of using these is to separate defense from pitching while still incorporating some measurement of how ‘fieldable’ the contact a pitcher induces is. Line drives are a little trickier for defenders to handle than ground balls, and tend to lead to more runs scoring. This is reflected in the runs/outs data we have for batted ball types, which leads the way quite neatly to tRA.

If you aggregate the tRA outcomes (K, BB, HBP, HR, + batted balls), and apply run/out values, you end up with expected runs (xR) and expected outs (xO). We can easily convert this to runs per nine innings by taking xR/xO*27. That’s tRA. Note that it is not on the familiar ERA scale, as I believe a defensive neutral statistic should expect defenders to have a league average error rate. League average tRA is typically in the high 4s.

Why use tRA? Well, it’s an interesting tool to supplement FIP with if you want to look at how hard a pitcher is being hit. It’s not a FIP killer by any means, and the difference between StatCorner tRA (using MLB AM classifications) and FanGraphs tRA (using BIS classifications) should tell you why: batted ball types are pretty subjective. However, they’re not wildly inaccurate, and using tRA, especially alongside pitcher batted ball information will give a better understanding of what exactly a pitcher is doing.

I’m very pleased tRA has made its way to FanGraphs, and I can’t say enough thanks to David Appelman for making it possible. I hope everyone finds it useful.

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Mike Ketchen
14 years ago

Quick question mostly from a fantasy perspective of a guy who has enjoyed a lot of success relying on FIP. Should a large difference be expected? and what is considered dominate in terms of tRA? For example Beckett has been very good and his FIP and tRA are about a whole run different. Does this then mean Beckett has not been as dominant or is his 4+ tRA actually really good?

Thanks for the help.

14 years ago
Reply to  Mike Ketchen

Part of it may be that FIP and tRA are in different scales, so they’re not comparable to each other. FIP/.92 and tRA are more comparable. Also, pitchers who give up line drives will get punished more I think in tRA, so high line drive totals can drive tRA up, like in the case of Beckett last season.

Jack Moore
14 years ago
Reply to  Mike Ketchen

2 quick easy translations from tRA to tERA (tRA on the ERA scale)

tERA = .92*tRA
or even easier
tERA = tRA – .35, but this breaks down at the extremes.

Basically, 92% of runs allowed are earned, and that tends to be around .35 runs in the case of most pitchers.