When Do Small Samples Become Meaningful?

The second week of April is an interesting time in the MLB season. We can no longer simply look at 2017 projections, as we have new, albeit limited, information. Plus, who wants to look back to where we were a week and a half ago. We have actual numbers to run with now.

At the same time, most of the numbers we have are nowhere close to meaningful. It can be fun to look at possible changes to individual players, but the articles have to be so laced with small sample size caveats that it can be distracting.

So how much longer do we have to wait until some of those statistics begin to stabilize? Thanks to the hard work of Russell Carlton over at FanGraphs, there is a general guideline for stabilization points for most metrics in today’s game. Obviously these points aren’t absolute, one player can take a bit longer to stabilize while another may be locked in right from the jump. But this analysis gives us some frame of references for statistical discussions.

Below we take a look at some of the first statistics that stabilize. In each case we identify a Rays player for whom that indicator is especially noteworthy. We also provide a projected date when the stabilization plateau will be reached.

Batters

60 PA: Strikeout Rate - Steven Souza Jr. (Game 16, April 19)

Strikeout rates are presumed to stabilize quickly, and that will be especially interesting for Rays fans who have been puzzling over Steven Souza Jr.’s newfound plate discipline. In Souza’s first two seasons with the Rays, he struck out more than a third of the time. Striking out may not carry as big a penalty for a hitter as we once believed, but a 33+% K rate makes it extremely difficult to post a serviceable on-base percentage.

So far this season, Souza has struck out less than 10 percent of the time (9.1% to be exact). With six walks compared to just three strikeouts over 33 plate appearances, Souza is over halfway to reaching the 60 plate appearance point. The news is good all around, as the plate discipline statistics from FanGraphs also show a decided difference in approach from Souza this season.

It’s early, yes, but with strikeout rate stabilizing so early, this could be great news for the Rays.

80 BIP (Balls in play): GB/FB Rate - Kevin Kiermaier (Game 27, May 1)

Ground ball and fly ball rates are also early to stabilize, and their tipping point should come some time around the end of April. Ground ball and fly ball rates can be especially telling for a player seeing an increase or decrease in power. While home run rates and home run/fly ball ratios take slightly longer to stabilize, looking at the elevation a player is getting on his swing can be extremely telling as to whether a power surge or power outage is simply a matter of bad luck or a change in swing plane.

For Kiermaier, we’re still a few weeks away from stabilization, but getting on top of the ball and hitting grounders regularly to start 2017. After a 2016 season in which he posted a career-high fly ball rate, he has seen a drastic change in profile so far this season.

This is likely the result of one week of baseball, but if it turns out 2016 was an outlier rather than a step towards a higher fly ball rate, Kiermaier may settle back in the 8-10 home run range rather than the 12-15 range for which he was projected coming into 2017. Kiermaier would still have plenty of value, of course, but it’s something to watch as the Rays play out the rest of April.

120 PA Walk Rate - Mallex Smith (Game 44, May 19)

This one is a lot further off, but worth noting. Smith may well see his name called for a minor league stint once Colby Rasmus returns, but if he doesn’t, sometime in mid-May it’ll be worth checking back in on his walk rate to see if he has been able to maintain it close to the 13.6 percent we’ve seen to start the season.

Smith did indeed have a double-digit walk rate throughout most of his minor league career, but the projection systems seemed to think major league pitchers would be more aggressive in their approach against Smith this season, giving him only an 8.0 percent projected walk rate for 2017. With Smith’s speed, any extra time on base has the potential to be a game changer, so even a dozen extra walks over the span of a season could be a big difference for Tampa Bay.

Pitchers

70 BF Strikeout Rate - Jake Odorizzi (Game 12, April 15)

Strikeout rates stabilize early for pitchers as well as hitters. Though Odorizzi is just two starts into 2017, he has faced 48 batters, putting him on pace to pace to pass the stabilization point for strikeouts in his next start - and the results haven’t been great.

Since his first full season in 2014, Odorizzi has seen his strikeout rate drop each year. He started with an excellent 9.32 K/9 in 2014, but as league-wide strikeout rates trended upwards, Odorizzi’sK/9 dropped to 7.97 in 2015 and 7.96 last season. Through 12.0 innings this season (which again, doesn’t sound like much, but is two-third of the way to stabilization), that figure is even lower, at 6.00 K/9.

Odorizzi has been able to achieve success despite the lower strikeout rates the last two seasons (4.13 ERA in 2014 compared to 3.35 in 2015 and 3.69 in 2016), but the question of sustainability is a fair one. While Odorizzi’s ERA dropped from 2014 to 2015-16, his FIP and xFIP rose. His above average BABIP and left on base percentage over the past two seasons suggest he could be a regression candidate heading into 2017. As a fly ball pitcher, Odorizzi will be as big a beneficiary of the Tampa Bay Super Outfield as anyone, but a few more strikeouts in the mix wouldn’t hurt.

70 BIP GB/FB Rate - Chris Archer (Game 16, April 19)

With 41 balls in play, Archer is over halfway to hitting this stabilization point. Archer’s early-season ground ball and fly ball rates aren’t far off his career rates. Over the past three seasons, Archer has seen his ground ball rate increase each year, a good sign for the 28-year-old.

If Archer can maintain a 50 percent ground ball rate, while keeping his elite strikeout rate, he should expect to have high levels of success. In 2016, only one pitcher had a ground ball rate over 50 percent to go along with more than 10.0 K/9: Noah Syndergaard. Even if we drop the K/9 to 9.0, only two pitchers were in that category (with Francisco Liriano joining Thor). Archer has the potential to join that elite group in 2017 if he can maintain his current worm-burning pace.