*This post originally appeared on insidethebook.com*

One of my favorite stats is RE24, which goes by other names, like “value added” or “value added by the 24 base-out states”.

The basic idea is that you are interested in the 24 base-out states, and the outcome of the performance in each of the particular states. A HR with bases empty has a different impact than a HR with men on base. A strikeout with a runner on 3B with less than two outs is hugely impactful, while with no one on base, it is no different than any other out.

To the extent that you think a player should be recognized for that outcome in that context, then RE24 gives you exactly that.

A decade ago, I wrote this little article, which focused only on the 8 base states (just for ease of explanation, and no other reason).

There is a useful chart there, and we can compare the first line (bases empty) to the second-to-last line (ROB, runners on base), so we’re only comparing those two states (was there a runner on base, or not). A HR for example is worth exactly 1 run with bases empty, but it’s worth 1.92 runs with a runner on base. While a single and walk have identical values with no one on base (0.29 runs), when you have runners on base, the single jumps up in value substantially (0.73 runs), while the walk adds a little (0.42 runs).

We see the K value has more impact than a regular out with a runner on 3B, -0.48 runs compared to -0.29 runs. (Note: since I lumped in all three out states, this gap is not as large as it should be, if I compared the K value with a runner on 3B and less than 2 outs. If you want to look at the full 24-base-out chart, there’s one right here. We see the biggest difference is when you have a runner on 3B and one out: the K value is an enormous -0.60 runs, while all other outs is -0.22 runs. In this situation, the pitcher is going to go out of his way to strikeout the batter. Of course, the batter is aware of this, and he’s going to go out of his way NOT to strikeout. There’s alot of these things game-within-a-game insight you will find with the Linear Weights by 24 base-out charts.

Anyway, to the extent you want to be aware of the impact of each event by these 24 base-out states, then the actual outcomes is captured in RE24. Given a large enough career, what we care about is RE24, and not Linear Weights (i.e., wRAA, wOBA, wRC+). That because RE24 is about outcomes based on the 24-base out states, while the other stats don’t care about the outcomes in specific states, and just assumes the performances were proportionately spread out.

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RE24 is especially helpful with relievers, as it properly assigns the run values when a reliever enters mid-inning and/or leaves mid-inning. For a starting pitcher (or a reliever that starts and ends his own inning) RE24 is proportionate to his runs allowed in any inning where he starts the inning and ends the inning.

While RE24 is compared to the league average (and so a pitcher that allows 1 run in two innings is going to get an RE24 of 0), you can simply add the league average runs per inning (say 0.500 runs per inning) to get the total number of runs allowed by the pitcher, and be exactly matched. (Though, you have to be aware of what particular RE24 chart is being used, as Fangraphs and Baseball-Reference use park-adjusted RE matrix.)

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I hope this helps those who are a bit flummoxed by exactly what RE24 does and how it is useful. In time, it should be part of your saber-arsenal.