Why Edward Jackson Should Be Bullpen Bound

Let me say this first -- both Edwin Jackson and Andy Sonnanstine should be in the rotation through the end of the 2008 regular season.  David Price is the only prospect with a chance to be an upgrade over them right now, and it's better for his development to be in the bullpen.

But going into the playoffs (knock on wood) and the 2009 season, I'd much rather see Sonny stick in the rotation and EJax moved to the bullpen (or traded for a right fielder).  There are two reasons.  One, Sonny is the better pitcher and two, Jackson would gain more by moving to the bullpen.

ERA, as has been discussed around here before, can be misleading.  Fielders determine the percentage of balls in play that go for hits, and batters determine what percentage of flyballs go over the wall.  There are three main skills that fall directly under pitcher control: K-rate, BB-rate, and GB-rate.  Striking out batters is good, because an out has been recorded without a chance of the ball finding a hole in the defense or a path out of the ballpark.  Walks are bad because they automatically put runners on base.  Groundballs are good, because they can never turn into homeruns.

In fact, a combination of these three skills is a better predictor of future ERA than ERA itself.  This predicted ERA is often called xFIP (eXpected Fielding-Independent Pitching).  You can also just look at the three skills on their own.  How do Jackson and Sonny stack up?  Here are eyeballed averages of their 2007 and 2008 performances:

Jackson: 6 K/9, 4 BB/9, 43% GB, 5.00 xFIP

Sonny: 6 K/9, 2 BB/9, 40% GB, 4.35 xFIP

Even though Jackson is a power pitcher, he doesn't strike out any more batters than Sonny -- he just walks more.  His 2008 ERA is only lower thanks to Rays fielders turning 5% more batted balls into outs for him versus Sonny.  Unless you think Jackson still has significant room to grow as a pitcher (and some do), Sonny is expected to post the better ERA going forward.

(Side note: both pitchers' have posted almost the exact same xFIP in 2007 and 2008, even though their ERAs are drastically lower in 2008.  They're not better pitchers this year, they've just had better luck and better fielders behind them.)

On to point number two.  On average, pitchers post ERAs a full run lower in the bullpen than in the starting rotation.  There are a few reasons for this -- they can throw harder for fewer pitches, they can feature only their best one or two pitches, and they don't need adjust to a hitter the second time through the order.  Earlier today, I asked RJ for his scouting report on both starters, without telling him why I was asking (although, he might be smart enough to figure it out.)  Tell me which one you think can take advantage of being a reliever more:

Pitcher A throws primarily a fastball and slider with an occasional change-up.  His fastball is in the low to mid 90s, but can be cranked up higher.

Pitcher B throws a fastball, cutter, slurve, and changeup.  His fastball sits in the high 80s.

I'd rather have Pitcher A (Jackson, in case you didn't figure that out) in the bullpen.  He can focus on his two best pitches and throw them harder.  Pitcher B wouldn't gain as much of an advantage because four pitches aren't needed and he doesn't have one or two that are significantly better than the rest.

So there you go.  Not only is Sonnanstine the better starter (by almost 3/4 of a run per nine innings) but his ERA wouldn't drop as much as Jackson's would by moving to the bullpen.  Would you rather have a 4.35 ERA starter and 3.75 ERA reliever or 5.00 ERA starter and a 3.50 reliever?  That's what I thought.

When the time comes to drop David Price into the rotation next season, or to move a starter to the bullpen for the 2008 playoffs, it's a no-brainer.  Sonnanstine stays and Jackson goes.