Besides Adrian Gonzales there hasn't been a player more impactful to their team as Jacoby Ellsbury is to this Red Sox line up. When he was placed on the DL last week citing back problems, the offense suffered, and it was noticeable. Over the last three games Ellsbury has played since returning, the top of the line up has been jolted. Elssbury's impact in the line up makes the Boston Red Sox better.
His steals are down this season (37) but his other numbers are up (.312 BA, 23 HR, 81 RBI). Not bad for a guy who was called "soft" by the Boston media and even some teammates last season. Andy Gresh of Boston's 98.5 The Sports Hub tweeted about him, calling him the five letter "P" word. Now Ellsbury has silenced them all, turning himself into one of the most complete players in the entire league right now.
His presence in the line up energizes those that even hit behind him(Gonzalez, David Ortiz, to name a few). Doing what he needs to do, which is be the catalyst for this lineup.
On the bases, he's still making opposing pitchers think because of his speed(A .369 OBP will do that).
Ellsbury has crossed the plate 93 times this season. The closest person to him, Adrian Gonzalez has 89.
Before people go on the tangent about how the Sox should get rid of Ellsbury, look at the numbers, and look at the way the team plays with him, and then take a look at how they play without him. This should be the easiest answer to anyone who watches Red Sox baseball or baseball in general. When a true catalyst is inserted, everyone feels it.