The Book Blog: MGL: Understanding DIPS

Where context is Jimmy Key.

Well, here is the deal. There ARE some pitchers who are true .280 pitchers.  And some that are even true .275 pitchers.  And possibly even .270 pitchers.  We already told you that when we told you that the SD of BABIP true talent among MLB pitchers was 7 points!  That means by definition that there likely are some of these pitchers in existence (not necessarily at the present time of course).  It is just that we don’t know who they are!  And there are so few of them, as compared to the many, many more who are near average, that if we find a pitcher who posts a low BABIP in 1 or even 2 or 3 seasons, it is much more likely that he is near average and got lucky than he is a true low BABIP guy.  So we just automatically assume that he is somewhere in between, but much closer to average.

Even though we might call him a .293 pitcher (say, .270 heavily regressed toward .300), what we really mean is that there is a 20% chance he is a .300 pitcher who got lucky, 15% chance he is a .299 pitcher who got lucky, a 10% chance he is a .298 pitcher who got lucky….all the way down to a 1% chance he is a true .280 pitcher, and a .1% chance he is a true .270 pitcher, exactly equal to his sample BABIP.”

So yes, he could be another Mo Rivera, who is likely 2 or 3 SD’s from the mean in BABIP.  But we simply don’t know that yet until we have 15 or 20 years from the guy at a .270 or .280 clip, and even then we are not 100% sure what he is.  At that point, the numbers will change to, “20% chance he is a .275 pitcher, 15% chance he is a .280 pitcher who got lucky, 10% a .285 pitcher who got lucky, etc.”