## Tuesday, April 29, 2014

### When does Small Sample Size stabilize - Hitters K%

As Aaron has touched on already, early in the season it's easy to get wrapped up in a poor start and think the sky is falling and forget that there's still a lot of season left for things to turn around. So, when do we reach the point where what we see is what we get? Is it a third of the way through the season, as we've heard the broadcast team say so many times already this season? Is it a month? Do we wait until the All-Star break? Well, at the risk of sounding like a cop-out, it depends. Thankfully, people much smarter than us have done the research and found the following stabilization points for various rate stats. You can't argue with science, right?

Baseball Prospectus has an excellent post that gets into the messy, mathy stuff, if you're so inclined. If you don't have a B-P subscription what's wrong with you FanGraphs has a more concise post on the same research. Here's the gist, lifted directly from FanGraphs:

• 60 PA: Strikeout rate
• 120 PA: Walk rate
• 240 PA: HBP rate
• 290 PA: Single rate
• 1610 PA: XBH rate
• 170 PA: HR rate
• 910 AB: AVG
• 460 PA: OBP
• 320 AB: SLG
• 160 AB: ISO
• 80 BIP: GB rate
• 80 BIP: FB rate
• 600 BIP: LD rate
• 50 FBs: HR per FB
• 820 BIP: BABIP
• 70 BF: Strikeout rate
• 170 BF: Walk rate
• 640 BF: HBP rate
• 670 BF: Single rate
• 1450 BF: XBH rate
• 1320 BF: HR rate
• 630 BF: AVG
• 540 BF: OBP
• 550 AB: SLG
• 630 AB: ISO
• 70 BIP: GB rate
• 70 BIP: FB rate
• 650 BIP: LD rate
• 400 FB: HR per FB
• 2000 BIP: BABIP
Generally speaking, until we reach the stabilization point for a given rate stat, we can expect a player to "regress" towards their career averages going forward. With those numbers in mind, I'm starting a series that will look at these stats as we reach the above listed thresholds to see what, if any, meaningful numbers pop out.

Today we'll look at K% for hitters, as seven Astros have reached 60 PA and another four are between 50 and 60.

 2013 K% 2014 K% Difference Career MLB Average During Career Altuve 12.7% 7.8% -4.9% 11.9% 19.5% Dominguez 16.3% 20.2% 3.9% 16.6% 19.5% Fowler 21.3% 22.3% 1.0% 22.3% 18.8% Carter 36.2% 35.9% -0.3% 34.8% 19.3% Castro 26.5% 27.8% 1.3% 23.5% 19.3% Villar 29.5% 28.2% -1.3% 29.1% 20.0% Presley 20.0% 19.1% -0.9% 19.3% 19.3% Krauss 30.8% 30.5% -0.3% 30.7% 20.0% Grossman 24.3% 30.9% 6.6% 25.4% 20.0% Springer 27.3% 28.3% 1.0% 28.3% 20.8% Guzman 24.8% 33.3% 8.5% 21.7% 19.0%
I threw career and MLB average rates in there for context. Also, since there's no history at the major league level, Springer's 2013 is from the minors. As we can see, most everyone is around 1% of last season and pretty close to their career average, with a few exceptions.

Altuve stands out for very positive reasons. He's cut way back on swings on pitches outside the zone this season, which is good as he's seeing fewer first-pitch strikes. Getting ahead in the count early is forcing pitchers to throw more hittable pitches in the zone.

Dominguez is on the other side of the pendulum. He's swinging at more pitches outside the zone, fewer pitches inside the zone, and making less contact on any of them. He's seeing a high percentage of first pitch strikes, getting behind early, and hasn't been able to make adjustments during the at bat.

Grossman is particularly worrisome. After seeming to figure things out after rejoining the club in July last season, he's seemingly gotten very passive. He's swinging at fewer pitches, and making less contact when he does swing. It was often noted after his return last year that he was more aggressive at the plate; it would seem that his struggles again relate to being too passive.

Which leaves us with Guzman. Guzman's K% has gone up every season he's been in the big leagues. This season his contact rate is actually up, but he's swinging at far fewer pitches, particularly in the zone. Opposing pitchers have already clued into this, and they're pumping 71% strikes in on the first pitch, putting Guzman behind from the get-go.