Ultimate Base Running (UBR) is a component FanGraphs uses to account for the value a player adds to their team via base running on non-stolen base plays. Much like UZR and wRAA, this run value is determined using linear weights, with each individual base running event receiving a specific run value. Base running isn’t a huge part of the game, but taking the extra base and avoiding outs of the bases can add a few runs a year.
To calculate UBR you need to know the average run expectancy for a given batting event given the base-out state and then the actual run expectancy change that occurred during the play. The best way to explain the calculation is to provide a simple example. Imagine there is a runner on a second and a single is hit.
The base runner can (essentially) stay at second, advance to third, score, or be thrown out. Each of those plays occurs across the entire league with some frequency. Let’s say 5-40-30-25% for those outcomes just for illustration. If you weigh all of those results by frequency and run value of each results based on run expectancy, you wind up with an average value for that situation. Let’s call it 0.7 runs, for illustration only.
In other words, if a generic batter hits a generic single with a man on second, the run expectancy for that inning goes up by 0.7 runs. To calculate a runner’s UBR for that particular play, you take the actual run expectancy change relative to the average run expectancy change for that event. So if the runner scores, that’s something like +0.9 runs, which is 0.2 runs above the average result and he gets that +0.2 value as UBR. To determine a player’s UBR you simply add up the value of all of their relevant base running plays. Unfortunately, we do not have play-by-play UBR data available on the site, so you cannot track it at a very granular level.
Mitchel Litchman’s primer outlines the different base running events that are accounted for in UBR:
1) On a hit, advancing an extra base, not advancing an extra base, or getting thrown out trying to advance an extra base, as long as no other base runner is blocking an advance.
2) A batter getting thrown out trying to advance an extra base on a hit (if he successfully does, we don’t know it, as he is simply awarded a double, for example, on a usual single where he advances an extra base).
3) On a hit, the batter advancing, not advancing, or getting thrown out when a runner is safe or out advancing an extra base.
4) Trailing runners advancing, not advancing or getting thrown out when a leading runner is safe or out trying to advance an extra base on a hit or an out. This is basically lumped together with #1 above.
5) Runners trying to advance on fly ball outs – i.e. tagging up.
6) As mentioned above, on ground balls to the infield, runners on first staying out of the force or DP at second base, whether the batter is out or is safe on a FC.
7) Also as mentioned above, a runner on second advancing or not (or getting thrown out) on a ground ball hit to SS or 3B.
Runners on third base advancing, not advancing, or getting thrown out at home on a ground ball are not considered (on air balls they are) [As of March 2015, WP and PB are now included in UBR!]
Base running is certainly not the most important tool in baseball, but you can improve your team’s odds or cost your team runs with good and bad base running. In order to properly value each player’s contributions, we need to measure their base running. The difference between standing on second or standing on third has value to a team, so we want to measure the difference between those two outcomes and given credit to runners who make it farther.
UBR allows us to do that by awarding base runners credit based on the run value difference associated with different base-out states for running that occurs when the ball is in play. Other sites use other particular methodologies but they all essentially work the same way. We want to account for the run value difference between various base running outcomes and credit runners who are more successful. But we don’t simply want to reward you for taking extra bases, we want to punish you for getting caught or not advancing in situations in which most runners advance.
How To Use UBR:
UBR is very easy to use because it is a simple run value above or below average, just like many other stats available at FanGraphs. If you are a +2 UBR player, that means you have added about two runs with your base running so far that season. Base running is generally a predictable skill, but there are not that many opportunities to really let your wheels show by taking the extra base. This means that 1) even the best runners can’t add more than 8-10 runs per year and 2) you can’t learn much from UBR over the course of a few dozen games. It is a very useful tool for measuring what happened, but you need a larger sample for it to tell you much about skill. A player who is consistently +5 UBR is almost certainly a good runner, but a player who is +0 one year and -6 the next year may or may not have gotten worse. A few bad plays could have cost them.
Please note that the following chart is meant as an estimate. No matter the year, this statistic will always have zero UBR as league-average.
Things to Remember:
● UBR does not account for stolen bases and caught stealings, which are dealt with by wSB.
Links for Further Reading: