The 'Day Banny' Phenomenon and the Royals Rotation

Brian, pitcher, sabermatrician, non-vampire

Do the Royals have anybody like Brian Bannister currently on staff?

It is June 23, 2010 in the nation's capital.  Stephen Strasburg, possibly the most hyped pitching prospect of all time and yet only 21 years old, left the mound after beginning his fourth start of his budding MLB career.  His meteoric rise to stardom began only a year prior as the first overall pick of the Washington Nationals.  Today, he was facing the lowly Kansas City Royals, 29-43, sagging under yet another depressing season.

Brian Bannister jogged to the mound to follow the phenom, took the ball, and began warming up with his bright royal blue glove.  Despite being one of the most likeable Royals in recent memory, Bannister, a pitcher who could only dream of Strasburg's raw physical talent, was a total mismatch for this game.  This would be his last year in Major League Baseball, and Bannister was in the middle of his worst professional season, three years removed from his best season in 2007.  Nobody in Washington expected the Royals to win.

However, the sun was shining--it was a day game.  Those around the Royals had hope, for Day Banny was going to the mound.  Day Banny was not just a mirage, but a marked phenomenon.  Over Bannister's career, he started 74 games at night and 40 games in the day.  At night, he was quite poor--a 5.68 ERA, an .808 opponent's OPS, a 1.64 K/BB rate.  However, in the day, he was a totally different pitcher, with a 4.04 ERA, .719 OPS against, and a 1.88 K/BB.

Bannister out-dueled Strasburg, shutting down the Nationals over 6 excellent innings and giving the Royals' bullpen a 1-0 lead.  Pitching wins and losses are statistically meaningless, but they still hold some emotional weight, and Strasburg suffered the first loss of his professional career to the Royals and Bannister.  I watched the game, and I remember it fondly to this day.

The 2014 Royals began this season with five straight day games and played an unusually high number of day games to start the season; after 24 games, the Royals had played an even number of day and night games, when the final count is usually a 2:1 ratio.  It got me thinking: was Day Banny a singular phenomenon?  Does the league have trouble with day games?  Do the Royals have a Day Banny?  Well, the results might surprise you.

***

In 2014, teams have played 1,272 night games and 684 day games.  During the night, the league is hitting .254/.319/.396/.714 and scoring 4.21 runs/game, while during the day, the league is hitting .246/.313/.384/.696 and scoring 4.05 runs/game.

That's about a 26 run difference over 162 games between two identical teams otherwise, or roughly 2.6 wins.  Over the past five years combined*, however, the difference is smaller, from 4.35 runs/game in the day and 4.36 at night.  Some years are worse than others, but the trend is pretty consistent, if small.

*Interestingly, there have been more and more MLB games played in the day; 1,564 day games where played in 2009 and 1,628 games played in 2013.  If current pace is kept, the MLB will have played 1,700 day games this year.

Why is this the case?  Perhaps a major league hitter (or Brian Bannister, if you're reading this) can for sure tell us why.  I only have a few guesses.  First, day games throw off ballplayers' preparation, and most of the time there is a day game immediately following a night game.  Since hitting is hard anyways, this might just give the edge to the pitchers who did not play the previous day.  Another possible reason is the sun/shadow factor.  As Ryan Lefebvre sais every time he gets a chance, it is difficult to hit the ball when it must go from shadow to light or vice-versa on the way to the plate.  This only happens in certain instances, but it can only happen in the day.

Regardless, that Bannister's ERA was over a run and a half different between day and night is certainly unusual.  And yet, it would seem that the Royals' current crop of pitchers ascribes to the Day Banny school of weird day/night splits.

***

Six Royals pitchers have made more than one start this season, and four of them have over 1,000 innings under their belt.  It is to these fine gentlemen--James Shields, Jeremy Guthrie, Jason Vargas, and Bruce Chen--that I will look to see if the Royals have a modern Day Banny.

The answer:  more than you would have thought.

Here are these pitchers' career day/night splits:

Pitcher IP ERA K/BB Slash IP ERA K/BB Slash
James Shields Day 690.0 3.43 3.42 .243/.294/.389 Night 1085.0 3.99 3.64 .265/.313/.429
Jeremy Guthrie Day 418.2 3.96 2.10 .256/.313/.430 Night 1080.2 4.34 2.00 .270/.326/.446
Jason Vargas Day 343.0 4.07 2.27 .256/.312/.415 Night 729.1 4.28 2.14 .262/.318/.424
Bruce Chen Day 494.1 4.35 2.24 .264/.328/.449 Night 1002.1 4.62 2.01 .263/.328/.457

Of these four, Shields has the largest gap between day and night ERA at .56.  Interestingly, though, every single pitcher is better during the day as opposed to the night.  While this does mostly rule out the possibility that any of these individuals are vampares, it does bring up a question.  Why?  It's a combined 1.42 earned runs/9 innings difference.

With Danny Duffy and Yordano Ventura, there's a lot more noise, but I'll include their numbers anyway:

Pitcher IP ERA K/BB Slash IP ERA K/BB Slash
Danny Duffy Day 56.0 4.34 1.53 .250/.350/.453 Night 148.1 4.43 1.68 .256/.348/.404
Yordano Ventura Day 11.0 4.09 2.25 .267/.327/.333 Night 74.2 3.13 2.83 .234/.293/.385

Yeah, hard to find any real information from 11 innings, but it will be interesting to see what happens to these two pitchers as their career grows longer.

This year, however, everybody seems to be bucking their career trends.  Vargas, Guthrie, Duffy, and Ventura are all giving up more runs in the day than at night.  Then there's Shields, whose day ERA is 2.42 and night ERA is 4.76 despite striking out almost five batters per walk after the moon rises.

Sometimes, baseball is a funny game.  Fortunately, that's what makes baseball baseball.

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