THE BOOK--Playing The Percentages In Baseball

Sunday, September 18, 2011

Do hitters and pitchers perform better during the day or at night?

All data from 1993-2010.

I look at each player’s game, and captured whether they were in the starting lineup or not, and which park they played in.  And of course, their wOBA.  I matched on those categories (starting or not, park), to make sure that the player pool was equally represented in day and night.  (That is, if Sosa had 1000 PA at Wrigley in the day and 2000 PA at Wrigley at night, then I counted Sosa with 1000 PA in each.)

For hitters in the starting lineup, their wOBA was .3429 in day and .3423 at night.  Basically, a match.  However, I then broke it down by “times through the order”.  And that’s where things became interesting.

Their 1st time through the order, it was 0.331 day, 0.335 night.  That difference, on 219239 matching PA, is 3.9 standard deviations from the mean.  The 3rd time (and later) through the order, it REVERSED, with 0.347 day, 0.344 night, or 4.0 standard deviations (going the other way).  If you think of day time as games playing from 13:00 to 16:00 and night as playing from 19:00 to 22:00, then it would seem that the optimal point to maximize offense is somewhere between 16:00 to 19:00.

Basically, the above data would be consistent with this idea.  If you peak at around 5 o’clock, then comparing your 1st time through the order performance (at 1 o’clock) in the day to 1st time through (at 7 o’clock) at night, we see an advantage for the night game.  However, your performance the 3rd and later time in the day (at 3 or 4 o’clock) to the same at night (at 9 or 10 o’clock) would give the advantage to the day.

Interestingly, for substitute players, we don’t see that!  The first time they come up, their day and night performances are a match (.305 in day and night).  This part makes sense, because they’d be playing at say 2 or 3 o’clock in the day and 8 or 9 o’clock at night.  Equidistant let’s say from 5 o’clock.  But, the 2nd and later time they come up, their performance in the day is .313 while it .329 at night, which is quite the reversal.  (Based on 4417 PA, which is 2.1 standard deviations from the mean, but in the reversed direction of the starting group.) Maybe these guys are subs for some particular reason, maybe they partied too hard, and didn’t recover for day games?  I dunno.

For pitchers, their performances are more consistent with the 5 o’clock theory.  Relievers, who would be pitching between 3 and 4 o’clock, perform with a wOBA of .328 in the day.  But at night, say after 9 o’clock, the wOBA drops to .324.  With 270287 PA, this is 3.7 standard deviations from the mean.

As a general rule, if you need to visualize it, your wOBA is going to peak at around 5 o’clock (maybe 6? someone else can figure it out), and the wOBA is going to drop by a point or two for each hour from that peak time.

This has some serious implication for the “times through the order” effect, and may provide partial explanation as for why starting pitchers perform as well as they do the 4th time through the order.