Thursday, July 18, 2013

Does the Homerun Derby REALLY mess up players swings?

I love posts that dispel myths of all sorts. After reading about the psychology of our love with fanciful stories (narratives) fueled by information that fits our preconceived notions versus solid data driven evidence (especially concerning economics and science) versus solid data driven evidence (especially concerning economics and science), its not hard to see how our worldly observations are heavily biased. We hate feeling conflicted; we hate to be wrong.

The baseball Home Run Derby is no different.

The myth goes like this: Most players who participate in the Home Run Derby will have their swings irrevocably altered the rest of the season resulting in a huge drop in home runs. 

A great post on Fan Graphs examines the data and found some interesting results that helps dispel this myth:  FANGRAPHS POST

The Home Run Derby is kind of counter-intuitive to many MLB managers. Old-schoolers like Mike Scioscia would rather his players did not participate, saying, “I haven’t seen somebody come away from that derby and be a better player for it.”¹ The Home Run Derby turns the team game into an individual competition. Players exhaust themselves and risk tweaking their swings, but has the derby really affected the second-half performance of its participants?

To answer this question I looked at what goes into a player’s stats. There is a lot of luck involved in baseball, so I took a look at the differences in the way players hit the ball before the derby compared to after the derby. Looking at the past five derbies, I calculated the average batted-ball flight for players that were healthy for both halves of the season

The HR to FB ratio drops considerably, and could explain a decrease in batting average and slugging percentage, as well as on-base percentage. It seems that players hit the ball the same way, just with slightly less power.

The large drop is ISO shows that indeed power does decrease for derby participants in the second half, and the overall line shows that players do perform worse. It’s not merely a function of hitting the ball to the wrong place, as the .oo6 drop in Bating Average of Balls in Play (BABIP) is not really significant. Players strike out a little bit more, but the notion that players change their swings and have trouble hitting the ball the same way after participating in the derby seems misguided when considering the small change in K% along with the consistent batted-ball percentages outlined in the first table.

So, NO CHANGE IN TYPES OF BALLS HIT. I speculate that (all other factors being equal) given the small 1% increase in strikeouts, the drop in power (home runs) in the second half of the season could be the result of fatigue.

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