Chan Ho Park and the Amazing, Unsustainable Home Run Rate

A glance at Chan Ho Park’s 2009 statistics can mislead. None of his aggregate stats stand out. His 4.43 ERA ranked below league average, a 96 ERA+, and his 9.1 hits per nine and 3.6 walks per nine led to an inflated 1.40 WHIP. Combined with his poor reputation, this might lead someone to believe that Park stunk in 2009. As Dave explained during the World Series, that opinion does not reflect Park’s mid-season transition. His overall stats suffered from his poor performance as a starter early in the season. The real story lies in his move to the bullpen in May.

Park produced horrible results from the rotation. Over seven starts, from April 12 to May 17, he lasted just 33.1 innings, or just about 4.2 per start. In that time he allowed five home runs while walking 17 and striking out 21, for a FIP of 5.42 to go with his ERA of 7.29. Some of that, at least, appears to be bad luck. In April, for instance, Park allowed four of those five home runs, but on just 20 fly balls. But even in May, with a lower HR/FB rate, he still allowed 14 runs over 18 innings while starting, walking 12 to 11 strikeouts. At that point the Philies rightly decided that Park’s stint in the rotation was over.

From that point on Park allowed zero baseballs to leave the yard. That covers 49 innings, including 38 fly balls. In that span he struck out 52 batters while walking just 16, for a FIP of 2.06, which undercut his 2.57 ERA. He allowed runs in just eight of 37 appearances, and allowed multiple runs just four times, more than two runs just once. Over July and August, in 16 appearances and 25.1 IP, he allowed just three earned runs, walking just five to 29 strikeouts. Clearly, the move to the bullpen did him wonders. But can we expect that again in 2010?

Apparently the Yankees, who signed Park to a one-year, $1.2 million deal with an additional $300K in incentives, think there’s a chance. Even accounting for a league average HR/FB rate in 2009, Park’s xFIP was still 4.02. There’s a chance, though, that Park continues to keep fly balls in the park at a below league average rate. It won’t be zero, but if Park can continue what he did in 2009, he might keep that HR/FB low. That makes him slightly less valuable, but considering his strikeout and walk rates in the bullpen we still might expect a considerably above average performance in 2010.

The Yankees’ hope is that something changed for Park in 2009, because his 2008 stint in the bullpen didn’t go as well. Over 70.1 IP he struck out just 49 to 28 walks, posting a 4.85 FIP, a full run higher than his 3.84 ERA. The drastic increase in Park’s strikeout rate and reduction in walk rate from 2008 to 2009 does suggest that something changed, though we’d be hard pressed to prove it.

We could look to his PitchFx data, but from what I understand the pitch classification algorithm changed from 2008 to 2009. That might partly explain Park’s reduced use of his four-seamer and the increase in his two-seamer. The only other major change I can see is the reduced use of his slider and the increased us of his changeup. But, again, this counts both his starts and relief appearances, so it’s difficult to draw conclusions. Looking at his pitch type chart, he does appear to have increased his changeup usage later in the season.

It’s always a risk when a team signs an aging pitcher who showed signs of improvement in limited duty the previous season, but the Yankees are in a position to take the gamble. Adding Park to the bullpen gives the Yankees even more depth, allowing them to perhaps trade one of Sergio Mitre and Chad Gaudin, or otherwise send Joba Chamberlain or Phil Hughes to AAA in order to build up their innings, rather than sending one to the bullpen initially. If Park pitches near his 2009 level, they’ll benefit from a stronger bullpen. If he flops, the can afford to eat the remainder of Park’s $1.2 million salary, like they did with LaTroy Hawkins in 2008.