Calculating Aaron Hill’s Expected BABIP

There’s been a lot of talk on how unlucky AHill has been this season. His .196 BABIP is one of the lowest in history (and in-fact is the lowest of the decade). But does he deserve this low BABIP due to his approach & linedrive percentage?

Two things we know:

1. Hill’s BABIP is EXTREMELY low at .196

2. Hill’s Linedrive Percentage is also extremely low at 9.9%

Question:

What is AHill’s expected BABIP when we take into account his low linedrive rate?

Figuring out Hits

Firstly, we want to strip out the home runs from Aaron Hill’s ball type data. According to Joe Lefkowitz’s Pitch F/X data, 24 of AHill’s HR’s have been flyballs. Only 1 was a linedrive.

We turned % into whole numbers, ie 9.9% linedrive is now 0.099. This number was multiplied into total BABIP style AB (431), which brings us to a rounded up 43 linedrives. We then subtracted AB that ended with HR, leaving us with 42 total linedrives in 406 non-HR ABs. Also subtracted are HR hit type, ie 24 flyball HR were taken from the 236 total flyballs.

AB per Hit Type:

From this data we see that AHill has hit 42 linedrives, 152 groundballs and 222 flyballs in play

AL Average

Baseball-Reference supplies ball type splits. 2010 AL Averages

As we can see, flyballs produce a batting average of .219 (automatically accounts for sac flies). But we want to strip out HR to get a roundabout flyball in play batting average. The end total BA balls in play on hit types:

Flyballs: .142
Linedrives: .719
Groundballs: .234

Taking those percentages and multiplying them into AHill’s batted ball hit type data leaves us with (hits):

Flyball: 31
Linedrive: 30
Groundball: 35

Grand Total of 96 hits

Now this leaves us with our slightly altered expected BABIP of:

.23645

AHill’s been unlucky in 2010 but his hit data shows that his expected BABIP of .236 based upon hit data is still a far cry from his career .300+ BABIP average.