tRA / tERA
Description:
Building on FIP, tRA includes batted ball types, namely line drives, ground balls, and the different types of fly balls. By assigning expected run and out values, tRA correlates better with following-year Runs Allowed per nine inngings than any of the other advanced metrics. tRA is on a R/9 scale so it will always be higher than ERA. It is on a Runs per nine innings scale because the creator, Graham MacAree, felt that since the statistic is based on league and defense neutral out values then defenders should be expected to have a league-average error rate. League average tRA is typically in the high 4s. tERA is the exact same thing, but scaled to ERA. To convert tERA to tRA, simply divide tERA by 0.92. tERA is more useful for comparing to ERA/FIP/xFIP as they are all on the same scale.
Context:
2009 tRA value continuum for MLB starting pitchers:
| Pitcher | tRA | tERA |
| Zack Greinke | 2.35 | 2.16 |
| Felix Hernandex | 3.28 | 3.02 |
| Johan Santana | 3.66 | 3.37 |
| Ricky Nolasco | 3.94 | 3.62 |
| Jason Hammel | 4.25 | 3.91 |
| Jeff Niemann | 4.77 | 4.39 |
| Jon Garland | 5.10 | 4.69 |
| David Price | 5.40 | 4.97 |
| Livan Hernandez | 5.82 | 5.35 |
| Armando Galarraga | 6.60 | 6.07 |
Things to Remember:
- tRA needs a large sample of expected outs to carry much meaning.
- tRA* has been regressed to league-averages in order to be useful in smaller samples.
- tRA values can be found at Statcorner.
- Batted ball classifications aren’t always 100% accurate since they rely upon a human scorer saying, “Yes, that looks like a line drive and not a fly ball.” It’s just a small caveat to keep in mind while using tRA data.
Links for Further Reading:
Intro to tRA – Technical Version
