Sacrifice flies have only been recorded in the major leagues since 1954 so it would be impossible for a player before then to have an OBP less than their batting average. Since that date, however, 160 players have pulled off the feat in a season. The highest number of plate appearances in a season on the list is 131 (Eddie Bowman, 1963). As might be expected then, most on the list are pitchers who don't bat very much and aren't generally known for plate discipline. However, the occasional position player (including Bowman) also shows up.
Only twenty-three players have eighty or more plate appearances in a season with an on base percentage less than their batting average. I've listed them below, as well as the players on the list for their 2007 season.
As I mentioned above, two players joined the full list of players last year. Livan Hernandez had a line of .213/.211/.267 in 79 PA for Arizona and Wladimir Balentien had a line of .667/.500/2.000 in a whopping four plate appearances for Seattle.
Only two players are on pace to join the list so far this year. One is Orioles hurler Garrett Olson with his .333/.250/.333 line in five plate appearances. Since interleague play is over, he is unlikely to hit again this year, barring a trade. The other player who may join the list is Arizona outfielder Alex Romero. In 38 major league plate appearances, Romero has a .229/.222/.286 line. He currently finds himself in AAA but may yet find his way back to the big club. Just another quirky thing to keep track of in the second half of the season.