I’ve taken some time to break down expected goals of each side in Argentina’s Primera División by offensive and defensive performance and by type of play.  I’ve decided to display the breakdowns in two charts for offensive and defensive performances, and I’m going to borrow a practice from Formula One to highlight performance extremes.

Below is the offensive performance chart for Primera as of Round 22.  The actual and expected goals are reported for open play events, set piece events, and penalties, and the most and least goals in each category are highlighted in purple and red text, respectively.

Below is the defensive performance for the Primera clubs.  The actual and expected goals allowed are reported for open play events, set piece events, and penalties, and the most and least goals in each category are highlighted in red and purple text, respectively.

Here are the main points:

• Boca have a narrow but persistent lead in the actual table, but they are a clear leader in expected goal performance on both sides of the football.  Through 22 rounds they have created 42.4 xG, a margin of +2.8 xG over their closest rival (Racing Club) and with 19.9 xG have allowed 2.1 xG fewer than anyone else (Defensa y Justicia are closest).
• No team comes close to Boca in the number of goals created and scored from open play.  Close to 90% of Boca’s goals have come from open play (40 of 46), and their expected goals from open play lead the league by a wide margin (+6.1 xG). Their return from set pieces, however, is more akin to a mid-table team – Temperley’s xG to goal performance in set plays is similar. But Boca’s strikers are so clinical in open play situations that it almost doesn’t matter.
• Boca is one of only two sides yet to be given a penalty (Arsenal de Sarandí is the other), but they have had just one penalty called against them, and none since the penalty in their Round 1 match against Lanús (which hit the crossbar).  This article in La Nación (in Spanish, of course) discusses Boca’s lack of penalties and suspensions as a contributor to their success.
• It looks like the closest challenger to Boca’s title run will be Newell’s Old Boys, which makes little sense on the surface.  They barely create more chances from open or set play than a typical mid-table side, and they actually rank 20th in overall offensive xG.  But their defensive xG is fantastic, and no club allows fewer than their 8.61 xG allowed from set plays.
•  Racing Club should be Boca’s challenger, but they aren’t and probably won’t.  They have the second highest offensive xG and the third lowest defensive xG in the league.  Their performance from open and set play appears balanced and their defensive performance on set plays is excellent.  The difference is that they have allowed 11.2 xG from open play and 19 actual goals from those situations — the widest gap for any team in the division save one (Vélez Sarsfield).