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Mookie Betts' production has dropped off in AA


Those of you who know what Mookie Betts has been doing this season in his first games in AA must think I'm crazy. This kind of production - a .418/.455/.658 line through 18 games - represents a drop off from the previous year? I would have thought it crazy too, until I looked at the numbers the night before last.

I was trying to test my idea that Betts' production this year is just the next incremental improvement in a year long trend of steady improvement. It had been reported that his numbers were .145/.340/.263 through May 2 of 2013, improving to .296/.418/.477 by the time he was done at low-A Greenville, and improving further to .341/.414/.551 over his 51 games at high-A Salem. Those numbers seemed to indicate steady improvement, which could mean that his current phenomenal production is no hot streak, but represents where he truly is in his development, and could therefore be expected to continue as long as he stays in AA. I wanted to see this trend more precisely. What I found was a bit surprising, but no less reassuring.

In looking at trends in player performance over a season, I like to look at the results for groups of about 18 games each. There are a few reasons I like the number 18 for this purpose.

For one, it's a very "baseball" number. It's the number of players in a game at any given time. It's the number of strikes in six strikeouts, which is the number of outs in an inning. And just as there are 9 innings in a game, there are exactly 9 groups of 18 games in a major league season.

It's also the number of games in six head-to-head series of typical length (3 games per series), my point being that the choice of a multiple of 3 is more attractive than a number that isn't because it means your group of games has a good chance of coinciding with a group of series.

This seasonal equivalent of an inning (a "seasoning"?) also encompasses a large enough sample to smooth out a player's splits. In other words, each batter will face a relatively balanced number of lefties versus righties, and play relatively balanced numbers of home versus road games, day versus night games, strong versus weak opponents, etc. One really excellent game, or one very poor game, won't skew the results a lot. Yet it's a small enough sample to give some detail about how a player's performance changes through the course of a season.

In analyzing Mookie's 2013 season, I deviated slightly from groups of 18 due to the number of games he played at each level. I chose to divide his low-A games into 4 chunks of 19 because it worked out balanced that way, and his high-A games into 3 chunks of 17 for the same reason. Then I compared these to the first 18 games of 2014.

Thanks to Baseball-Reference.com for the game logs that allowed me to do this.

Here are the results:

Game group

G

BA

BABIP

OBP

SLG

low-A 1

19

0.172

0.164

0.349

0.313

low-A 2

19

0.348

0.339

0.471

0.652

low-A 3

19

0.315

0.367

0.402

0.521

low-A 4

19

0.338

0.407

0.434

0.408

high-A 1

17

0.230

0.214

0.258

0.426

high-A 2

17

0.333

0.380

0.453

0.492

high-A 3

17

0.459

0.446

0.543

0.738

AA 1

18

0.418

0.423

0.455

0.658

Betts BA and OBP

You can see that the batting stance adjustment he made for the fifth game of the second group (that is, on May 5, 2013) paid immediate dividends. Things leveled off for a bit then, but when promoted to high-A there was a clear initial drop off, and an equally clear recovery. Then a very strong finish to the season. So strong, in fact, that this year's oustanding .418/.455/.658 start through 18 games represents a dropoff in performance.

For some reason his slugging percentage had a drop off in the latter half of his games at low-A Greenville, and so the dropoff in the jump to high-A Salem doesn't appear. Otherwise, the trends are the same:

Betts SLG

Is the dropoff at the start of 2014 not actually a dropoff, but rather due to a random fluctuation in Mookie Betts' results? It could be small enough of a change for that. Or it could indicate his adjustment to a new, higher level of baseball. And if it does, we can expect his current level of production to not only continue, but to get better.

If it is indeed an actual level-adjustment dropoff, then I'd expect him to hit at least .450 with an OBP over .500 over the next 15 games. And that would just be really amazing. And probably the end of his AA career.

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