More on defense
April 5, 2007 1 Comment
Since my article posted, some interesting things have come out of some discussions around the internet, like here on Baseball Think Factory and here on The Book Blog.
We found out that the difference in plays made between the two systems is line drives. Stats has been counting line drives caught by infielders as plays and opportunities in zone, where BIS is only counting ground balls. In the days when I only had zone rating and a fielder’s traditional stats (PO, A, DP, E) I tried to estimate chances using assist and DP’s. For 3rd basemen, they always had a few more plays made than assists (middle infielders did not have this problem, since they rack up assists as the middle man in a DP, which does not count in zone rating). Third basemen are almost never the middle man in a DP (maybe once a year on an extreme shift like they do for Ortiz, Giambi, and Bonds), yet third basemen had 15-20 more plays than assists every year. I thought it might be field the ball, step on 3rd forceplays, by it always seemed that play should be more rare. Now I know they are line drives.
The next question that troubles me is that STATS generally counts a few more balls as in zone than BIS, but for some shortstops its a few plays, for some its 30 plays, and for a very few BIS actually counts more plays in zone than STATS does. I’m not sure if this is just a random distribution caused by different zone definitions, or it points to data or scorer quality issues. Something to look into in the future.