On-base Percentage Anomaly
Saturday, March 27, 2010The calculation for On-base Percentage (OBP), the stat with a misleading name, leaves a small chance for a very odd stat line. There is a very slim chance that a batter can have a lower OBP than batting average (AVG). How does this happen? Well, lets take a look at the calculations for OBP and AVG:
AVG: H / AB
OBP: (H + HBP + BB) / (AB + BB + HBP + SF)
OBP adds BB, HPB and BB back into the formula, so getting walked or hit by a pitch raises a batter's on-base percentage since the two stats are on both sides of the division. However, Sacrifice Flies (SF) are also added to the calculation, but only in the denominator. So, every sacrifice fly actually lowers a player's OBP. A player with virtually no BB or HBP and several sacrifice flies will actually have a lower OBP than their batting average.
As impossible as this sounds to achieve, it has actually happened in the Major Leagues. Take a look at Phil Niekro's 1982 batting stat line. In 91 plate appearances, "Knucksie" had 17 hits, 1 sacrifice fly and was not walked or hit by a pitch. This gave him 87 at bats. Let's calculate his AVG and OBP:
AVG = 17 / 87 = .195
OBP = (17 + 0 + 0) / (87 + 0 + 0 + 1) = 17/88 = .193
Of course this anomaly will likely only happen to pitchers in the Major Leagues, but it still makes for an interesting stat line!