30 March 2018

Are Sinkerballers Affected by the Team's Spring Training Location?

On Tuesday, the Baltimore Sun had an article about Andrew Cashner and how he feels coming into the season.  It read:
Cashner said having spring training in Florida for the first time in his career — he trained in Arizona when with the San Diego Padres and Rangers – allowed him the opportunity to get a better feel for his sinker.
“You go to Arizona and you really don’t have a chance to work on your sinker because it really doesn’t sink there, so I think I really had the chance to work on it all spring,” Cashner said. “I feel like I’m in the best place I’ve been in a long time with my breaking ball.”
I have not seen this suggested before and it is a fairly interesting idea.  If you are unable to see the outcome of your pitches, it might well be difficult to get ready.  Last year, Cashner threw a sinker 54% of his pitches, so he certainly would be a prime candidate to be impacted if this is a real effect.

I looked at seasons from 2015 through 2017 for pitchers who threw sinkers 40% or more of the time.  I considered these pitchers to be heavily dependent on sinkers.  For Florida, the data set contained 23 player seasons.  For Arizona, the data set contained 28 player seasons.  A few players are counted twice for their separate seasons.  The metrics I used for comparison were FIP and wOBA.
40% SI/2S FIP wOBA
April Rest April Rest
Florida 3.70 4.00 .296 .319
Arizona 4.35 4.32 .317 .320
t-test 0.34 0.26
The data is messy.  That is the first thing to notice.  In general, it appears that Florida sinkerballers see their performance erode past the first month while Arizona sinkerballers remain the same.  However, none of the data here is significant (t-test).  If this was a significant finding, it would perplex me a little bit.  The narrative should be that Florida pitchers would remain constant while Arizona pitchers improved.  We do not see that.  Really, the only aspect that came up with a significant t-test was when we compared Florida pitchers wOBA for April to the rest of the season (0.02).  They performed better in that month and then significantly reduced their performance.

I decided to take another stab with, of course, worse data.  I looked at pitchers with a sinkerball rate greater than 50%, which is more representative for the kind of pitcher Andrew Cashner is.  At first, I took a subset of the above dataset, which was a far reduced amount of data.  A couple weird things emerged, so I thought it was best to increase the data set.  For this, I looked at seasons 2011 to 2017.  This yielded 17 Florida player seasons and 23 Arizona player seasons.
50% SI/2S FIP wOBA
April Rest April Rest
Florida 3.61 3.83 0.296 0.317
Arizona 4.04 4.02 0.301 0.312
t-test 0.42 0.59
And, so we got more of the same, which is not interesting and also a little bit interesting.  It is interesting that we again observe an insignificant decrease in FIP for the Florida pitchers while the Arizona ones are level.  We then see a significant increase in wOBA for the Florida pitchers (0.05).  Meanwhile, nothing else seems to emerge from the data.

So, what we might be seeing is just a weird artifact that will disappear with a larger dataset.  Strangely, what we do not see is what Cashner appeared to claim we would see, which would be a poor handle in the beginning of the year and then improvement.  The only thing that might be happening is that for some reason sinkerball pitchers who train in Florida seem to come out of the gates very strong in the first month and that advantage appears to escape them as the year progresses.


Unknown said...

John, your data are very interesting, but I think your interpretation is wrong. You forgot about weather-related factors - in April it tends to be cold, the ball doesn't fly, and run scoring is suppressed. One could argue that sinkerballers should be the least significantly affected by this phenomenon, but it certainly can't be argued not to exist. A quick glance at the 2017 numbers show that the MLB-wide average ERA was 4.09 in March/April and 4.41 for the rest of the year. In light of this discrepancy, it looks like your data show exactly what Cashner suggested - relative to the rest of the league, sinkerballers who train in Florida remain consistent throughout the season, experiencing a performance regression as the weather warms up commensurate with the league average, while sinkerballers who train in Arizona improve relative to the league as they move deeper into the season.

Jon Shepherd said...

Maybe. I think the analysis to consider that would require more than that comparison.