In my “Baseball Resume” post I talked about my abysmal AVG and my much better OBP. Most of you probably know that AVG stands for batting average (sometime abbreviated BA). Still, if you are new to the game, there’s nothing wrong with not knowing. OBP stand for On Base Percentage.
These stats are very similar. Both measure offensive consistency. Both are measured out to the thousandth place (.000) and range from .000 (worst possible) to 1.000 (perfect).
There are a number of differences though. AVG is determined by dividing the number of hits by the number of at-bats. OBP is determined by dividing the number of times a player reaches base safely by the number of plate appearances.
Seems like same thing? Almost, but not quite. A plate appearance (PA or TPA for total plate appearances) is any time a player walks up the plate and either becomes a runner or makes an out. There are a number of results where a plate appearance does not count as an at-bat: sacrifice bunt (SAC), sacrifice fly (SF), base on balls or walk (BB), and hit by pitch (HBP). These distinctions are made to protect a batter’s average for sacrificing himself or for the inability of the pitcher to throw three balls over the plate.
There are two results that will hurt a players AVG but increase their OBP: error (E) or fielder’s choice (FC). Both of these are results where it is judged the player should have been out, if the defense had not failed to make the play (E) or chose to make another play (FC).
Most players will have a higher OBP than AVG. Where a great hitter has a batting average over .300, most teams want their leadoff hitter, whose main job is to get on base for other batters to drive him in, to have an OBP in the upper .300s or even .400+.
To show just how far apart the two stats can be, last season Chipper Jones lead the MLB with a .365 AVG and a .470 OBP. The .105 difference was mainly to due to his 90 walks.
Note: Although I do not know of an instance in MLB history, it is technically possible for a player to have a higher AVG than OBP. This would require the batter to have at least one hit, and more sacrifice bunts and/or sacrifice flies than walks, hit by pitches, fielder choices, and errors combined. As you can guess, this is extremely unlikely.