Tuesday, December 7, 2010

HOME COOKING

Yesterday in my post about the Shaun Marcum trade, I commented how I felt that hometown players tend to be overrated and thus, to the Brewers benefit,  the Toronto Blue Jays over spent for Brett Lawrie.  In the comments, Kyle offered a very compelling rebuttal:

"Being a MN resident Brewer fan I disagree. The money and fandom brought in by Joe Mauer is probably well calculated by the team. They get way more tickets and merchandise with Mauer here. That Mauer value is useless to all other teams besides the Twins but if I own Joe Mauer and am not the Twins I am going to attempt to extract that value when trading him and if I am the Twins I will put it in the equation."
That's keen analysis.  Perhaps there is some collateral benefit of having home town players on your team.  I'm guessing that the Brewers sold more Craig Counsell t-shirts than Joe Inglett t-shirts last year.  Did they sell any more tickets?  Perhaps to his friends.  But still, I can buy into what Kyle is saying.

So then, how large must this collateral benefit be in order to offset - if I'm right - the lesser quality of play that a team is willing to accept from a home town player, compared to a comparable replacement player that they could instead have?  In order to answer that, I must know the difference in the quality of play.

I created a database of every U.S. born hitter who played in the Major Leagues from 1961 to present - the "expansion era".  The list includes over 43,000 seasons and over 2 million games played.  Then I flagged each season as to whether the player was playing for a team in the same state in which he was born.  Here are the compiled results:


BASLGOBPOPSBB/K
Playing at home
0.262
0.403
0.331
0.733
0.62
Playing away
0.258
0.396
0.324
0.719
0.57

I guess I was wrong.  Players who play for teams in their home state actually play a bit better than those playing away from home.  The differences are not large, but with as large a sample size as we have, they are real.  I'm surprised by that.

In my tally, 11% of the games played were by home-state players.  That strikes me as much higher than what you would expect if players were distributed randomly.  There is an apparent concerted effort by teams to acquire locally born players.  I guess we already knew that.

There might be a bit of selection bias in the data.  For example, Cal Ripken played his entire career in his home state.  All of his stats are included in the "Playing at home" row.  Barry Bonds was born in California.  But those two players combined make up less than 3% of that whole row.  There are some good players on the other side too. I don't think the differences would be enough to sway the findings.

I don't know if the same holds true for pitchers.  If I get curious enough, I'll figure it out.

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