When To Worry About Hyun Soo Kim...Not Any Time Soon

Kim's First Spring Training Hit Orioles Hangout

This spring, Hyun Soo Kim is 1-24 with only three strikeouts (the one hit being an infield single).  That is rather impressive to get out so often on a batted ball.  I have yet to see him play, so I do not know about the quality of the batted balls.  However, it seems that they might mostly be rather weak contact.  This might cause some concern for people who were expecting him to play a major role in left field this season, but how valid is that worry?

Last year, Matt Wieters was coming off his arm injury and was 0-23 with a walk.  That performance did not appear to reflect his performance during the season.  Wieters was certainly still getting back to playing form and was unable to catch consistently at that point, so maybe the comparison is not exactly apt.  That said, Kim is adjusting to a new league, a new culture, and even a new Spring Training setup that is condensed from the Korean three-month norm to that American standard of about 33 days.  Some might remember last year when Jung Ho Kang also had a long acclimation period that was as bleak as Kim's current experience.

We can try to discern something by taking a quantitative approach.  Looking only at MLB season production, Russell Carlton found that the only indicator that might be useful with less than 100 PA (which no one ever achieves in Spring Training) is strikeout rate.  Nothing else reflects season numbers beyond that metric.  I would argue though that when we see Kim not performing, we are not trying to discern what his seasonal average will be.  What we are trying to figure out is more of an up-down conclusion.  Will Kim be good or not?

As a quick first look, I looked at all of the players with rookie status in 2014/2015 and compared their performance in Spring Training against their performance during the regular season.  Very simply, I bucketed the 60 players into three groups with ascending Spring Training slugging percentage. 

Bucket	sOBP	StDev	sSLG	St Dev
1	.300	.034	.382	.069
2	.312	.032	.410	.062
3	.312	.033	.406	.059

Traditional standard of significance (0.05) was not met, but Buckets 2 and 3 were far more similar than Bucket 1 was with either 2 or 3.  In other words, Bucket 1 gives the incredibly noisy appearance of being different than Buckets 2 or 3.  However, if you look at even five or six of the players in Bucket 1, that vague difference will in no way give any suggestion that there are differences.  I would say that this initial test informs us that there is not a great reason to think there are differences, but further investigation should be considered.

I next tried to see how important the Spring Training data was for predicting actual results in conjunction with a projection model (i.e., ZIPS).  The result there was that Spring Training data account for less than 2% of the final performance.  For players with slugging below .400 during Spring Training, the contribution to the model rose up to 4%.  In other words, trust ZIPS. That model has Kim at 272/338/424.  If Kim goes 0-60, then this model would adjust him down to 270/335/420.

Keep in mind that this is a pretty rough cut to answer the question.  Players that were awful and simply were assigned to the minors are not included here.  The players within this population were seen as meaningful enough to stay in the majors for a considerable amount of time.  That likely results in a survivor bias.  That said, we see similar effects for players who greatly excelled in Spring Training.  If we were to think that Spring Training provides enough meaningful events to discern how poorly one might do, then we should probably be able to discern how well someone might do.  I could not establish that with this data.