LOB%
Left on Base Percentage (LOB%) measures the percentage of base runners that a pitcher strands on base over the course of a season. This stat does not use the left on base numbers reported in box scores, but instead is calculated using a pitcher’s actual hits, walks, and runs allowed results:
LOB% = (H+BB+HBP-R)/(H+BB+HBP-(1.4*HR))
Most pitchers have LOB%s around league average (which is approximately 70-72%, depending upon the season), and pitchers that deviate from that average tend to see their numbers regress towards average in the future. In other words, if you see a pitcher with a 60 LOB%, they are letting lots of runners score so their ERA will be high, but the odds are that they will strand more runners in the future and lower their ERA.
Not all pitchers will regress toward league-average, though: high strikeout pitchers have been shown to have some control over their LOB%. Pitchers that record a high numbers of strikeouts can pitch their way out of jams more easily than pitchers that rely upon their team’s defense, so they are able to maintain LOB%s higher than league average. Also, if a pitcher isn’t a major-league caliber starter — or if they’re a borderline case — it’s likely that their true-talent LOB% is below league average.
By using this statistic in conjunction with others — specifically BABIP and HR/FB — it’s possible to get an idea of if a pitcher is under- or over-performing and likely to regress. For more details, see the two videos below:
Context:
Please note that the following chart is meant as an estimate, and that league-average LOB% varies on a year-by-year basis. To see the league-average LOB% for every year from 1901 to the present, check the FanGraphs leaderboards.
| Rating | LOB% |
|---|---|
| Excellent | 80% |
| Great | 78% |
| Above Average | 75% |
| Average | 72% |
| Below Average | 70% |
| Poor | 65% |
| Awful | 60% |
Links for Further Reading:
Piper was the editor-in-chief of DRaysBay and the keeper of the FanGraphs Library.
I doubt anyone will see this any time soon, but why the -1.4*HR?
I had the same question. The article “Left on Base” from the Hardball Times hints at the reason. My understanding is that LOB% here is somewhat similar to FIP in that both assume that HRs are within the control of the pitcher. When a player hits a HR, roughly 1.4 runs are scored on average, or this was at least this was the average at one time. And so similar like BABIP, LOB% is trying to look at how a pitcher’s luck has played out regarding bases empty vs. runners on base. For example, a pitcher with an LOB% over 85% would likely be getting lucky and his ERA would likely be lower than his FIP.
Some interesting examples of this are happening right now with Justin Verlander and Hyun-Jin Ryu. In Verlander’s case, he is sporting an amazing LOB% of just under 94% right now through ~80 IP (it was at 97%(!!) before his last start), and his ERA is 1.30 lower than his FIP, 2.38 to 3.64. He has been giving up a lot of HRs this year (which will happen with the high heat) but because a lot of them have been solo shots it hasn’t skewed his numbers as much as one would assume. Outside of those occasional dingers he has been super stingy with the walks (17) and hits (42), with a crazy 0.74 WHIP.
In Ryu’s case, he is just not allowing any walks (he’s issued FOUR in 65.1 IP), and while he isn’t punching out as many guys as Verlander (just 65 for Ryu to JV’s 95), his WHIP is also insanely low at 0.83, and his LOB% is just below Verlander at 92.1%. He has a much higher BABIP (.259 to JV’s .165), but hasn’t been plagued by the HR problem Verlander has. But, like JV, his ERA is almost a full run lower than his FIP- 1.65 to 2.59. So here are two guys that are- for now- exceptions to the general rule. It will be interesting to see how the rest of their seasons go.