Ellsbury vs. Coco

Can someone please tell me why Ellsbury is not in the lineup?  Does Coco have a better average against Sonnanstine?  He is a right handed pitcher, so I can't really see why it is necessary to take Jacoby out, and i'll tell you why.  Jacoby had the third best average on the team in the regular season (determined by how many at-bats.)  Coco not only had a worse average in the regular season, but he doesn't produce in the postseason either.  Maybe a certain game 6 of the 2007 ALCS would remind you?  He was taken out and Jacoby was put in.  And he came through.  And he will do it again.  Even Francona said in last nights press conference that he could tell Ellsbury was almost through his small slump. Jacoby has a better arm than Coco, and more speed.  Ellsbury is the reason we score, when he's on base, we get runs.  Give me feedback on this decision please, cause i'm sure I don't know all of the details on who's better against Sonnanstine.  Thanks :)