Posted by Matt Sisson on Tuesday, August 4, 2009 at 8:42 pm

Throughout the years, Dan Haren has been one of the best first half pitchers in baseball.  But then that midway point hits and he begins to lose what made him so good in the beginning of the season.

Here’s a look at the numbers:

Dan Haren: 1st & 2nd Half ERA’s

So what’s causing this shift?

Well in 2008 batting average against went from .211 to .294, SLG against (SLGA) rose from .332 to .443, and his BABIP rose from .256 to .375! In 2007, Haren saw similar increases.  BAA rose from .316 to .396, SLGA rose from .327 to .478, and his BABIP rose from .234 to .357.  More of the same in 2009;  so far Haren’s BAA increased from.189 to .240, SLGA from .311 to .410, and BABIP .233 to .273.

Many of these increases can be attributed to Haren losing velocity towards the end of the season.  FanGraphs shows the average and range of velocity of Haren’s pitches over the last three seasons using Pitch-fx data.  Towards the end of the season, the range and average drops for a majority of the starts for his pitches, rebounds for a game or two, and then drops.  This would suggest that the Haren loses the ability to throw hard on a consistent basis as the season nears the end.  The drop may only be a few miles an hour but that can make a world of difference.

Now may be the time to trade Haren in you fantasy league…I did last week.