On-Base Percentage (OBP) measures the most important thing a batter can do at the plate: not make an out. Since a team only gets 27 outs per game, making outs at a high rate isn’t a good thing — that is, if a team wants to win. Players with high on-base percentages avoid making outs and reach base at a high rate, prolonging games and giving their team more opportunities to score.
The formula for OBP is simple:
Generally, you can swap out the denominator for PA without much issue, but little things like sacrifice bunts and catcher’s interference aren’t included so it won’t be perfectly equivalent.
OBP was a big leap forward ten or twenty years ago because it gave credit to hitters who reached base via walk or HBP when batting average ignored those things. Any time you don’t make an out, you’re contributing positively to the run scoring process and OBP captures that better than batting average because it incorporates a big slice of offensive activity that batting average doesn’t consider. Getting on base via walk doesn’t help your team quite as much as getting a hit, but it’s certainly valuable enough to warrant inclusion in even the most simplistic metrics.
OBP has become synonymous with the book “Moneyball” because at in the early 2000s, teams weren’t properly valuing players with high OBPs and the Oakland A’s could swipe talented players for cheap because they were one of the few teams paying attention to walk rate. These days, every team has come to accept how vitally important OBP is to their success, and that particular “market inefficiency” has been closed.
How to Use OBP:
OBP reads like batting average, but because it incorporates walks, OBPs are about 60 points higher on average. So the equivalent of a .300 hitter should have a .360 OBP or so.
Getting on base is an important skill, so you want to use OBP to determine if the player in question is a good offensive performer. However, OBP can only take you so far and it should only be used in the context of other statistics because OBP weights every time you reach base equally, whether you hit a home run or an infield single. If used in conjunction with slugging percentage or isolated slugging percentage, OBP is a very useful tool. In general, something like wOBA or wRC+ will tell a more accurate story, but if you’re looking for something extremely simple OBP is a much better bet than batting average.
Please note that the following chart is meant as an estimate, and that league-average OBP varies on a year-by-year basis. To see the league-average OBP for every year from 1901 to the present, check the FanGraphs leaderboards.
Rules of Thumb
Things to Remember:
● OBP is considered more accurate than Batting Average in measuring a player’s offensive value, since it takes into account hits and walks. A player could bat over .300, but if they don’t walk at all, they’re not helping their team as much as a .270 hitter with a .380 OBP.
● A player’s OBP is a good predictor of their future OBP after 500 plate appearances. So if Pujols has a .500 OBP after only 50 plate appearances, don’t expect him to continue reaching base at that rate.
● OBP treats every type of hit and walk equally, meaning that a player who goes 2-4 with two singles will have a .500 OBP but a players who goes 1-4 with a home run will have a .250 OBP.
Links for Further Reading: