Marlins Sign Heath Bell

From Fangraphs:

However, before any team ponies up for Bell’s services, I’d hope that they’d ask themselves just how much of Bell’s success will follow him if he leaves San Diego.

It’s no secret that Petco Park is the best place in baseball to pitch, and specifically, that it is almost impossible for left-handed batters to hit home runs there. After all, park effects aren’t a new or controversial subject, and there’s not much subjectivity in the data – pitchers who ply their trade in San Diego post numbers that they simply can’t post in other cities. Their numbers – especially in the area of home run prevention – are artificially deflated by the environment in which they pitch half of their games.

Bell is one of the signature beneficiares of how the park plays. In his career, he’s faced 791 batters in San Diego – 10 of them have managed to hit the ball over the wall, one for every 79.1 batters he faced. Away from the friendly confines, he has faced 1,182 batters and allowed 20 home runs, one for every 59.1 batters that have come up to bat against him. His home run prevention has been 34 percent better in San Diego than in all other ballparks, which of course makes perfect sense, given that he’s a right-handed pitcher and fly balls to right field in Petco have almost no chance of reaching the seats.

The park hasn’t just deflated his home run rate either – his career BABIP in San Diego is just .269, but his combined average against on balls in play in all other parks is .334. His BABIP away from San Diego is likely higher than his true talent level, and I wouldn’t suggest that teams should expect Bell to become eminently hittable upon signing with a new team, but the evidence shows that Bell has never been able to perform well on balls in play in any stadium besides Petco Park. At the minimum, that has to be concerning.

If Bell had been able to maintain his peak walk and strikeout rates in 2011, perhaps these tidbits would just be footnotes, but his K% fell from 30.0% in 2010 to 19.9% in 2011. It wasn’t just that Bell decided to throw more strikes, either – his contact rate jumped from 73.6% to 81.8%. Relievers are prone to variance in all status due to the small quantity of innings that they throw, so Bell’s regression may prove to be more outlier than sign of drastic decline, but it can’t be considered a good sign for his future that the one skill that should travel best took a big step in the wrong direction last year.

Bell’s never been a great command guy, but his combination of high strikeout rates and minuscule home run rates have more than made up for his propensity to issue a few walks. Unless a team also figures out how to sign Petco Park simultaneously, his home run prowess almost certainly won’t follow him to a new city, and so the strikeout rate would have to return to elite levels for Bell to maintain his status as a top-notch closer. It’s possible that his downturn in strikeout rate last year was a fluke, but is it really a good idea to bet a three year deal on a 34-year-old reliever hoping that his most recent K% isn’t a sign that he might be on the downside of his career?