What is Zone Rating?

What is Zone Rating?

Basically, ZR is the percentage of balls fielded by a player in his typical defensive ‘zone’, as measured by STATS reporters.

The first part of understanding Zone Rating is understanding how the field is divided up.

The field is divided into 22 equal ‘slices’.  Each slice runs from home plate to the outfield fence.  The first slice running along the left field line is Zone ‘C’.  (Zones A, B, Y and Z are in foul territory).  The last zone is Zone ‘X’. Like any ‘pie’ slice, or wedge, gets wider as you approach the outfield wall.  Zone C is about 7 feet wide at the third base bag, and about 20 feet wide at 300 feet from home plate.
The next 21 zones (D - X) divide the field equally until you get to the right field line.  The dividing line between zones M and N runs right over second base, splitting the field in half.

STATS ZR zone grid

With this division of the field understood, ZR becomes much easier to visualize.

For infielders, only ground balls are considered for zone rating.  Line drives, pop-ups and fly balls are not included.  This serves to, oh so slightly, under-rate the defensive value of all infielders, but presently this information is not readily available.  First basemen are responsible for all bunts that travel more than 40 feet and land in his area of responsibility.

Zones of Responsibility

While each ball is recorded for location, distance and speed, not every ball is a defensive player’s responsibility. That is, only balls that could reasonably be fielded from a typical defensive position are considered to be in a player’s zone.

Infield

First Base: The first baseman is responsible for covering zones V through X, the three zones closest to the right field line. This includes all grounders hit within approximately 25 feet of the right field line, and anything right up the line as well.

Second Base: The second baseman is responsible for zones O through T. The left boundary of Zone N is second base, so the right boundary (about 8 feet from second) is where the second baseman’s zone starts, and runs up to Zone U. Notice that Zone U is not in anyone’s zone. It is ‘the hole’ on the right side and not an infielder’s ‘responsibility’.

Third: The third baseman is responsible for covering zones C through F, the four zones closest to the left field line. This includes all grounders hit within approximately 35 feet of the right field line, and anything right up the line as well.

Shortstop: The shortstop is responsible for zones H through L. The right boundary of Zone M is second base, so the left boundary (about 8 feet from second) is where the shortstop’s zone starts, and runs up to Zone G. Notice that Zone G is not in anyone’s zone. It is ‘the hole’ on the left side and not an infielder’s ‘responsibility’.
 
Outfield

Outfielders are assigned two zones: one for line drives and one for fly balls. Since line drives aren’t in the air as long, they have smaller zones.

For a ball to be assigned to an outfielder, it must travel a certain distance. Corner outfielders are responsible for all line drives in their zones that travel between 280 and 340 feet. They are also responsible for all fly balls and popups that travel over 200 feet. The center fielder is responsible for all line drives between 300 and 370 feet and all fly balls and popups over 200 feet.

The left fielder is responsible for Zones F through H on line drives and C through I on fly balls and popups. Zone J between the centerfielder and left fielder is unassigned.

The center fielder is responsible for Zones L through O on line drives and K through P on fly balls and popups.

The right fielder is responsible for Zones S through U on line drives and Zones R through X on fly balls and popups.  Zone Q between the centerfielder and right fielder is unassigned.

On line drives, the zones J and Q are unassigned between the outfielders, while on fly balls, those zones are covered.

Using these zones, STATS determines how many balls are hit into each fielder’s area of responsibility. An infielder’s zone rating is equal to the number of outs made divided by the number of balls hit into the player’s zone. ‘Outs Made’ equals every ball fielded within the zone that is turned into an out, plus all balls fielded outside the zone turned into an out.  When a player fields a ball outside his zone and turns it into an out, it is counted as both an out and a ‘ball in zone’ for the purposes of calculating his zone rating.  This is a flaw in ZR, as balls outside the zone should be counted only as an out.  Otherwise it takes away a “range” aspect of the rating.

An outfielder’s zone rating is equal to balls hit into his zone which do not result in hits, divided by the number of balls hit into his zone. The player is credited with both an ‘out’ and a ‘ball in zone’ for balls caught outside his zone, just like the infielders.

This explains exactly how the zones are defined.  The reason these zones were selected is because these are the zones where balls are turned into outs at a greater than 50% rate.  The greater zone is not so much arbitrary, as drawn from a reasonable expectation that a fielder should make the play, since his peers do.