What is BAbip in Baseball?


Hello and welcome back to First Line Sports Analytics on YouTube! In this video, we’ll be talking about BAbip in baseball. We’ll look at what it is, what it can do, and the assumptions made by the metric. 

So, what is it? BAbip stands for batting average on balls in play. It is the percentage of balls a batter or batters put into play that become hits. So, as the name suggests, it is just a batting average, but only for balls hit into play. Meaning, it doesn’t include at bats that result in a strikeout, walk, hit-by-pitch, catcher interference call, sacrifice bunt, or home run. The equation is Hits minus home runs (because they’re never truly in play for the defense) divided by at-bats plus sacrifice flies (because they don’t get scored as at-bats) minus strikeouts and home runs again. The equation is just calculating the hits off of balls in play and dividing it by the number of times the ball was put in play. This can be calculated using box score stats.

So what can you do with BAbip? Well, it can offer insight into a batter’s ability to be successful when they put the ball out into the field. But it’s also very influenced by the luck of a ball falling in the right place, and also on the quality of the defense in the field. Per fangraphs.com, an average BAbip is about 300. And it’s most often that, if a player has a BAbip considerably different than 300 in the short term, it is most likely due to good or bad luck and/or consistently good or bad defense faced. In that case, the metric can show insight into why that player’s batting average or on-base-percentage is simultaneously abnormal. But, in the long term, larger deviations from that 300 average may suggest impressive or poor control at the plate.

For pitchers, it can show insight into the part of the game of which they have very little control. The BAbip of all batters against a pitcher has similar qualities to the BAbip for a single batter. In the short term, it can show abnormalities in luck or defense while the pitcher is in the game. In the long term, it can start to show the quality of the balls in play that the pitcher regularly allows.

Lastly, we’ll go over the assumptions made by this metric. As always, if a metric makes assumptions that you are not comfortable with, you do not have to use it.

The only assumption made by this metric is that it offers insight into a batting situation. 

This may seem silly, but it’s actually very important to understand. All sports metrics share the general assumption that the value produced will show insight into a chosen situation. What gets tricky is figuring out when that statement is true. As mentioned before, this metric can suggest different conclusions given how much data are being drawn from. 

Fangraphs.com suggests that it takes approximately 800 balls in play to get a sense of a batter’s real BAbip talent, and 2,000 balls in play for a pitcher’s. So, until that threshold is reached, it will be tough to figure out exactly what a BAbip value will be good for. It’s rare that it won’t be helpful at all, but it can be varying degrees of helpful in describing a couple different situations.
Rob (Part 7) – So, in summary, BAbip is the percentage of times that a ball-in-play results in a hit for a batter or group of batters. It can be used, in the short term, as an indicator of luck or defense in a given batting situation. In the long term, it can be an indicator of a batter’s hitting control or a pitcher’s ability at letting up batted balls in play. But, figuring out what this metric is trying to tell you and when is crucial in deciding whether to listen to it.

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