LOB% Definition

LOB% stands for left on base percentage. This is a statistic which measures how frequently a pitcher strands runners on base and it can be a helpful way to determine if a pitcher is over- or under-performing his true talent level.

The Concept of LOB%

The concept behind tracking LOB% is that this stat tends to normalize across most pitchers over time, much like BABIP tends to normalize near league-average for hitters. From year to year, the league average for LOB% tends to hang around 72%.

When a pitcher is significantly above or below that mark, it’s worthwhile to take a closer look. Is the pitcher just getting lucky (or unlucky), or is there a tangible reason for their deviation from the norm? Although most pitchers will end up near league average over a large enough sample, not everyone will fit that mold.

For instance, strikeout pitchers tend to be better at stranding runners on base, since they have that strikeout weapon as a possibility when in a tight jam. On the other hand, pitchers who are overmatched in the big leagues will struggle to hold runners on, as they’ll give up a large volume of hits and runs in general.

Why is LOB% Important?

If a pitcher has a league-average strikeout rate, but is stranding runners at a higher rate than expected, it’s likely that pitcher will come ‘back to earth’ in the near future. For instance, a pitcher with a low ERA and an unusually high LOB% is likely to see that ERA move up as their LOB% normalizes.

For an example of how LOB% can be used as an indicator of future performance, let’s look at how the fortunes of a pitcher changed between 2017 and 2018. The pitcher in question is Jon Lester, one of the game’s best pitchers for a decade by the time the 2017 season arrived.

In 2017, Lester’s ERA was unusually high at 4.33. He was still striking out batters at a high rate, nearly one per inning, so that skill was just as strong as it had been throughout his career. Looking at his 2017 stat line, it is the LOB% that stands out. Lester had a LOB% of only 68.7%, the second-worst mark of his career.

Knowing he was stranding such a low percentage of runners, expecting Lester to bounce back in 2018 would have been logical – and that’s exactly what happened. In 2018, his LOB% popped back up to 80.3%, and his ERA dropped to 3.32 as a result.

This attests to how big of an impact variance and randomness can have on a player’s performance, even across an entire season.

How is LOB% Calculated?

At least Compared to other advanced metrics, the calculation for LOB% is rather simple:

LOB% = (H+BB+HBP-R)/(H+BB+HBP-(1.4*HR))

As long as you have access to basic baseball statistics for a given pitcher, you can calculate his LOB% in just a matter of moments. You will only need to retrieve the following stats in order to complete the calculation:

H = Hits
BB = Walks
HBP = Hit By Pitch
R = Runs
HR = Home Runs

What is a Good LOB%?

Earlier, we mentioned that 72% LOB is where the league average tends to land from year to year. As you can see, the players listed below managed to beat that number by a significant margin in 2018.

Not surprisingly, many of these pitchers are known to be some of the best strikeout pitchers in the game, as the ability to record strikeouts is a huge advantage when trying to strand runners on base.

Highest LOB% 2018 Season, Min. 1IP per Team Game Played

Player	LOB%
Blake Snell	88.0%
Justin Verlander	85.3%
Mike Fiers	84.2%
Kyle Freeland	82.8%
Aaron Nola	82.5%
Jacob deGrom	82.0%
Max Scherzer	81.3%
Jon Lester	80.3%
Zack Greinke	80.2%
Jameson Taillon	79.8%

What are the Problems with LOB%?

LOB% is a useful tool, but it does not paint an entire picture on its own. You might be tempted to say that a certain pitcher has been lucky because he is stranding a high percentage of runners for the season, but that performance could be skill-based rather than just good fortune. You’ll need to dig deeper and look at other stats, such as strikeout percentage, to understand why the pitcher has been stranding so many runners.