THE BOOK--Playing The Percentages In Baseball

Wednesday, January 07, 2009

Line Drives

Brian says:

In Arlington, a batter is 18% more likely to have a batted ball coded as a LD, which may have helped Milton Bradley to have the 2nd highest LD rate in 2008 - while in Minneapolis, it’s 20% less likely. Four of the lowest six LD rates belong to Michael Bourn, Geoff Blum, Ty Wigginton and Hunter Pence, and Minute Maid Park has the second lowest LD park factor at 0.82. This is not saying that Houston batters hit fewer line drives - it’s that Houston and it opponents both have 18% fewer balls scored as liners in Houston than they do on the road.

Right.  A “line drive” is not necessarily a line drive.  If hitters are showing as hitting 20% fewer line drives in the Metrodome than away from the Metrodome, we don’t know if it’s because the Metrodome depresses LD rates, or if it’s because the scorer in Minnesota is depressing it.  Since it makes a huge difference when looking at LD and FB rates, then you need some sort of park factor to normalize the data.  If there is a systematic bias (say when it’s a FB pitcher, or when the balls are hit to RF), then you need a more sensitive normalizer.

All to say that if you have subjective data, then you need to determine if the discrepancy in the data is random or systematic, and then apply your adjustments accordingly.

Taking a guess, I have to believe this is a scorer issue.  A line drive is really a batted ball that leaves the bat at a certain angle, at a certain velocity.  I don’t see how those things would affect whether a ball is a LD, FB, or GB, regardless of the park you are in.  I can see how the scorer can be influenced by the positioning of the fielder (and worse, if the fielder caught the ball ornot), and try to assign a batted ball code.