Category WPA through 4/19
Here are the current Red Sox WPA breakdowns, through Wednesday's blowout of the Devil Rays. This chart shows the contribution of Red Sox starting pitching, relief pitching, and position players. The data for position players includes their contributions on both offense and defense. My WPA tracking assigns most of the defensive WPA value to the pitcher, but I assign a portion to other fielders in the case of exceptionally good or bad plays (based on my subjective evaluation).
The current chart highlights the dominance of the starting pitching this year, with quality from the bullpen as well (the overall staff ERA of 3.76 currently leads the AL).
The offense has started to kick in over the last three games, finally crossing into positive territory last night, but clearly it has been the pitching that has been winning games so far this year.