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K/9, BB/9

Postby Yoda » Thu Jun 07, 2007 8:58 am

The case against K/9 and BB/9:

The Case Against K/9 and BB/9

May 31, 2007

By Chris Constancio

A few visitors to this site have asked why we no longer include strikeouts per nine innings (K/9) and walks p nine innings (BB/9) in pitchers' statistics tables. The simple answer is that there is no need to; K% and BB%, or the number of strikeouts or walks per batters faced, are better descriptors of pitchers' skill in striking out batters and avoiding walks.

You might be wondering why it matters at all. It's true that both sets of numbers will give you similar information about most pitchers. For some pitchers, however, the differences can be meaningful. Let's take a look at how Kevin Slowey, who is scheduled to make his major league debut tomorrow, compares to other Triple-A pitchers in strikeouts per nine innings:

Name K/9
1. Yovani Gallardo 12.5
2. Virgil Vasquez 10.6
3. Jeff Niemann 9.6
4. J.A. Happ 9.4
5. J.P. Howell 9.0
6. Andy Sonnanstine 9.0
7. D.J. Houlton 8.5
8. Matt Garza 8.3
9. Colby Lewis 8.3
10. Ron Chiavacci 8.3
11. Jason Hammel 8.3
12. Kevin Slowey 8.0


Slowey is ranked #12 in strikeouts per nine innings. That puts him among the top 25% of qualifying pitchers, but he's still within one standard deviation from the average.
Here are the Triple-A pitchers ranked by strikeouts per batters faced:


Name K%
1. Yovani Gallardo 34.9%
2. Virgil Vasquez 27.9%
3. Andy Sonnanstine 25.4%
4. Jeff Niemann 24.5%
5. J.A. Happ 24.4%
6. Kevin Slowey 23.4%
7. J.P. Howell 23.4%
8. Colby Lewis 23.0%
9. Jason Hammel 22.8%
10. D.J. Houlton 22.8%
11. Matt Garza 21.9%
12. Ron Chiavacci 21.5%


This ranking paints a different picture. Both Slowey and Andy Sonnanstine have impeccable control, and they both move up a few spots when we rank pitchers by K% rather than K/9. Pitchers who do surrender many hits or walk a lot of batters have inflated K/9 rates because they face more batters per inning and therefore have more opportunities to record strikeouts. Six of the eleven pitchers ranked ahead of Slowey according to K/9 are not really striking out batters more frequently than Slowey; they are simply facing more batters per nine innings of work.

K% and BB% do a better job of isolating the skills they measure, so it should come as no surprise that K% and BB% are more strongly correlated from season-to-season than K/9 and BB/9.

If you are more comfortable understanding K/9 and BB/9 than K% and BB%, you can quickly get a feel for the range of these numbers by browsing the league leaders tables. As a general rule of thumb an average professional pitcher will strike out about 15% of opposing batters and walk about 8% of opposing batters.

K/9 and BB/9 will probably persist if only because fans are comfortable using these numbers and 'innings pitched' is a more widely available denominator than 'total batters faced'. But the numbers are available here and many other places as well. There is just no reason to use K/9 or BB/9 when analyzing a pitcher’s abilities.


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Re: K/9, BB/9

Postby jake_harv88 » Thu Jun 07, 2007 9:23 am

Nice read ;D Notice how the list is dominated by Devil Ray pitchers
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Re: K/9, BB/9

Postby The Jury » Thu Jun 07, 2007 9:32 am

Cool, thanks.
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Re: K/9, BB/9

Postby J35J » Thu Jun 07, 2007 10:15 am

Good read, I like it!
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Re: K/9, BB/9

Postby acsguitar » Thu Jun 07, 2007 10:26 am

MMM Yovani Gallardo %6 :L
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Re: K/9, BB/9

Postby J35J » Thu Jun 07, 2007 10:39 am

I will say I saw a comment about this on that site that is also true..... K/9 is more helpful for fantasy players while K% is more helpful for "real" life. Either way, I like it and will use it and will continue to use K/9.
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Re: K/9, BB/9

Postby talan37 » Thu Jun 07, 2007 11:25 am

I don't think k/9 is necessarily more "relevant" for fantasy... because as it points out a guy who pitches worse can have more k's.... while you could use the simple measure of k's of how a pitcher is going to do for your fantasy team, it would seem more relevant to consider his overall performance, which is is better indicated by his k%.(Ie. a guy with a high k/9 could get it by having a high whip(more walks + more hits = more batter faces = more k's))

Example:
Bad pitcher A has a k% of 10%, over the course of x innings faces 100 batters, and gets 10 strikeouts.
Good pitcher A has a k% of 20%, over the same x innings faces 50 batters, and gets 10 strikeouts.
If:
Good pitcher A pitches poorly, and over the same innings faces 100 batters, he will get 20 strikeouts...

They have the same k/9 technically. But which is more relevant to fantasy, and which would you rather have?...this is an extreme example, but you get the point.
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Re: K/9, BB/9

Postby J35J » Thu Jun 07, 2007 11:32 am

talan37 wrote:I don't think k/9 is necessarily more "relevant" for fantasy... because as it points out a guy who pitches worse can have more k's.... while you could use the simple measure of k's of how a pitcher is going to do for your fantasy team, it would seem more relevant to consider his overall performance, which is is better indicated by his k%.(Ie. a guy with a high k/9 could get it by having a high whip(more walks + more hits = more batter faces = more k's))

Example:
Bad pitcher A has a k% of 10%, over the course of x innings faces 100 batters, and gets 10 strikeouts.
Good pitcher A has a k% of 20%, over the same x innings faces 50 batters, and gets 10 strikeouts.
If:
Good pitcher A pitches poorly, and over the same innings faces 100 batters, he will get 20 strikeouts...

They have the same k/9 technically. But which is more relevant to fantasy, and which would you rather have?...this is an extreme example, but you get the point.



I'm just saying this mainly because Slowey isn't a strikeout pitcher....he's just got impeccable control. He'll be up the K% rankings because of this but it is a little misleading because he won't be a high K guy in the bigs. Anyway, like I said, I'll be using both!
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Re: K/9, BB/9

Postby talan37 » Thu Jun 07, 2007 11:57 am

You may not think his stuff will translate into the bigs... but saying hes not a strikeout pitcher is a bit of a stretch.

In 2.5 years and 305 minor league innings, he has 304 strikeouts. Thats a k/9 of 9. Hardly anything to scoff at....Hes being compared in that column to the BEST of the best in the minor leagues in terms of strikeouts.

Randy Johnsons minor league numbers:
417innings, 445Ks. A difference surely, but not a vast difference. In addition Johnsons Era and Whip were MUCH MUCH higher so he had a lot more chances to strike batters out.

Do I think hes going to be randy johnson... no probably not, but based on his statistics I wouldn't say its beyond the realm of possibility for him to become a "strikeout pitcher", and In the minors he certainly was. If you took his control out of the equation, and he faced say... 20% more batters, he would have 360 strikeouts in 305innings.... Thats why the K% is a bit more relevant.

For the record I didn't use randy johnson other than that he popped into my head as having a very succesfully career, and had a lot of K's, I don't mean to compare there styles or types or anything of that nature.
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Re: K/9, BB/9

Postby J35J » Thu Jun 07, 2007 12:20 pm

talan37 wrote:You may not think his stuff will translate into the bigs... but saying hes not a strikeout pitcher is a bit of a stretch.

In 2.5 years and 305 minor league innings, he has 304 strikeouts. Thats a k/9 of 9. Hardly anything to scoff at....Hes being compared in that column to the BEST of the best in the minor leagues in terms of strikeouts.

Randy Johnsons minor league numbers:
417innings, 445Ks. A difference surely, but not a vast difference. In addition Johnsons Era and Whip were MUCH MUCH higher so he had a lot more chances to strike batters out.

Do I think hes going to be randy johnson... no probably not, but based on his statistics I wouldn't say its beyond the realm of possibility for him to become a "strikeout pitcher", and In the minors he certainly was. If you took his control out of the equation, and he faced say... 20% more batters, he would have 360 strikeouts in 305innings.... Thats why the K% is a bit more relevant.

For the record I didn't use randy johnson other than that he popped into my head as having a very succesfully career, and had a lot of K's, I don't mean to compare there styles or types or anything of that nature.



Trust me, I love Slowey. He's a K pitcher in the minors because he has great command and is a better pitcher than most of those guys are hitters. There are many, many great command pitchers in the minors with very good K numbers but if they don't have top end stuff those numbers don't translate into the bigs. I like Slowey and think he will be a very solid MLB pitcher but I don't think his minor league K numbers will follow him up to the bigs, thats all.
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