FanPost

IsoD - Quantifying Plate Discipline

IsoD, for those of you who are unfamiliar with it, is short for "Isolated Discipline" and is calculated by OBP-AVG. It basically tells you what percentage of plate appearances result in a walk for that particular player. It tends to go along with IsoP (Power), which is SLG-AVG.

In my limited evaluation of players, IsoD and IsoP are the true measures of a player's talent. There's always some baseline batting average, but you can dismiss most of the fluctuations in that to BABIP. Issue is, this only really works for more experienced players (more stats to look at).

Let me give you somewhat of a numerical example.

Derek Jeter had one of the worst seasons of his career in 2008, and if you look at strictly OPS, it WAS the worst of his career. Does this mean that he's washed up and done for? Well, let's take a look at the numbers.

As I mentioned earlier, BABIP (lucky drops, gaps, etc) can account for year-to-year fluctuation in a player's batting average. If that player's IsoD and IsoP are consistent with his career norms, then I wouldn't read too much into a drop in OPS.

In 2008, Jeter batted .300/.363/.408, good for an OPS of .771. Not really great (especially if you take his defense into account), but a .300/.363 player is hardly something to sneeze at. Argue salary on your own time.

Anyhow, Jeter is a career .316/.387/.458 batter. So his batting average is a bit lower than his career numbers. Let's look at his IsoD. For 2008, it's .363-.300, or .063. For his career, it's .387-.316, or .071. So comparing .071 to .063, we're really not talking about a massive difference, only .008. If you look at his career IsoD's (per season) and get the standard deviation on them, that shows up as .010. That just means that this IsoD fluctuation is within a year-to-year fluctuation.

The thing that somewhat interests me is the fact that his AVERAGE is down .016 AND his IsoD has dropped. It should also be noted that his career IsoP is .142, and in 2008, it was only .108. That's a more significant drop.

To perhaps explain the low Average, we can look at his BABIP (Batting Average on Balls in Play). In 2008, Jete's BABIP was .336. That's high, compared to league average, but when looking at an individual batter, you want to compare it to his career BABIP instead - which is .361 for the Captain. 

What have I gleaned from this? Something is happening with Jeter outside of simple fluctuations, or at least something happened in 2008. 

From this point, we've determined his power swing has diminished. Turn him over to the team Strength and Conditioning coach, get him some Wheaties, get him to work on putting the ball into the gap. He'll be fine.

But I never settle at this. Anecdotal evidence is nice, but can I tie numbers to this situation?

My last (easy to find) source is his Plate Discipline data, which is generously provided by Fangraphs.com.

In 2008, Derek Jeter swung at 23.7% of balls outside of the zone, which is only a 1.8% increase from the previous season. However, this number is up 8.2% from 2005, when Jeter posted a healthy .389 OBP (and a .080 IsoD along with it). To complement the increase in out-of-zone swinging, his contact rates outside of the zone ALSO went up 18.6% since 2005 (Out-of-zone contact can lead to poorly hit balls, resulting in doubleplays, etc - unless your name is Vlad Guerrero, then it's a HR). His in-zone discipline has remained right about the same from previous years.

So what have we learned just from looking at like 8 numbers on Fangraphs? Well, 1. We know he's gotten unlucky, based on the .025 drop in his BABIP. 2. We know he's getting a bit impatient, from both his low IsoD, and his increase in swinging at (and making contact with) balls outside of the strike zone.

So now when your Yankees fan friend comes up to you and says "hey you're a big [expletive] baseball stat dork, tell me why Jeter [expletive] my [expletive][expletive] last season" and you can say "Well, let's see. He isn't walking as much as his career average (IsoD!) and he isn't hitting the ball for as much power as normal (IsoP!), maybe he's just getting impatient (Swinging %!!!)"

Look at you, you sabermetrician, you!

Eat. Drink. Be Merry. But the above FanPost does not necessarily reflect the attitudes, opinions, or views of Purple Row's staff (unless, of course, it's written by the staff [and even then, it still might not]).

X
Log In Sign Up

forgot?
Log In Sign Up

Please choose a new SB Nation username and password

As part of the new SB Nation launch, prior users will need to choose a permanent username, along with a new password.

Your username will be used to login to SB Nation going forward.

I already have a Vox Media account!

Verify Vox Media account

Please login to your Vox Media account. This account will be linked to your previously existing Eater account.

Please choose a new SB Nation username and password

As part of the new SB Nation launch, prior MT authors will need to choose a new username and password.

Your username will be used to login to SB Nation going forward.

Forgot password?

We'll email you a reset link.

If you signed up using a 3rd party account like Facebook or Twitter, please login with it instead.

Forgot password?

Try another email?

Almost done,

By becoming a registered user, you are also agreeing to our Terms and confirming that you have read our Privacy Policy.

Join Purple Row

You must be a member of Purple Row to participate.

We have our own Community Guidelines at Purple Row. You should read them.

Join Purple Row

You must be a member of Purple Row to participate.

We have our own Community Guidelines at Purple Row. You should read them.

Spinner.vc97ec6e

Authenticating

Great!

Choose an available username to complete sign up.

In order to provide our users with a better overall experience, we ask for more information from Facebook when using it to login so that we can learn more about our audience and provide you with the best possible experience. We do not store specific user data and the sharing of it is not required to login with Facebook.

tracking_pixel_9351_tracker