Calculating Basic Baseball Stats - on Base Percentage (OBP)

If you're a baseball fan, you probably are aware of how important statistics are to the game. A casual fan probably understands what most of the most popular statistics measure, in a general sense, but they may not know how to calculate these stats for themselves. Let's look at a one of the most basic hitting statistics and see how it's calculated.

On Base Percentage (also called On Base Average or OBP or OBA for short) is fast gaining respect among serious baseball fans as a very important indication of a player or team's value. The statistic takes batting average, which is the percentage of at bats in which a batter gets a hit, and expands upon it to, adding in the batter's ability to draw a walk or otherwise get on base, as well. On base percentage is basically the percentage of all times a batter goes to the plate that he gets on base. Since getting on base (in other words, not making an out) is the only way you can score a run, and scoring runs is the object of the game, on base percentage is a very important statistic.

To on base percentage, take the total number of hits a player has, and add the total number of walks and hit by pitch to that number. Next, that total by the total number of at bats, walks, hit-by-pitch, and sacrifice flies). On base percentage is displayed as a decimal, with three spaces after the decimal point.

For example, say a hitter got 157 hits in 500 at bats. The hitter added 75 walks, was hit by a pitch five times, and had 4 sacrifices. You'd calculate the equation like this:

157 hits + 75 BB + 5 HBP / 500 AB + 75 BB + 5 HBP + 4 SF = .406 OBP

To understand what this means, you can always think about OBP as a percentage or a ratio. In other words, a hitter with a .406 on base percentage reached base in 40.6% of his trips to the plate, or a little over 4/10ths of the time.

Now, what makes a good on base percentage? Well, it's generally accepted that a .400 on base percentage is pretty darn good. Of course, that doesn't mean a hitter with an OBP lower than that isn't a good hitter, or that you'd always want to pick a hitter purely on his on base percentage. There are other things to keep in mind (such as power and ability to drive in runs) that are captured in other statistics, such as slugging percentage.

The league average for batting average fluctuates from year to year, but has been around .340 in the past decade or so. In 2005, the league leaders in batting average were Todd Helton of the Colorado Rockies in the National League at .445 and Jason Giambi of the New York Yankees in the American League at .440.

Barry Bonds racked up the highest on base percentage since 1900 in 2004, when he compiled a .609 OBP, breaking his own record, set in 2002 at .582. The previous record holder had been Ted Williams, who compiled a .582 mark in 1941, the same year he became the last .400 hitter. Williams also holds the record for highest career on base percentage, at .482. Williams led the league in OBP twelve times.