Here is the (much) longer explanation of why I think the Brewers R/G average is inflated relative to other NL playoff contenders.
I will illustrate the point I’m making using the Brewers and Phillies as an example. Using just runs per game, going into play on Saturday, the Phillies are averaging 4.66 runs per game to the Brewers 4.50. That’s not a huge difference; the Phillies have scored 29 more runs than the Brewers and have played 2 more games.
But I have been looking at how the NL playoff contenders have performed against the 6 NL teams that are allowing more runs per game than the league average of 4.42: Rockies, Nationals, Reds, Pirates, Cubs, and Diamondbacks. Not coincidentally, these teams, along with the Marlins, have the worst W-L records in the league. I am intentionally excluding the Marlins from this discussion because their pitching has been pretty good. Their R/G allowed of 4.20 is slightly better than the Brewers’ 4.32. A team doesn't get any expected bump in run production by playing them.
Using the tables on Baseball Reference that list each team’s wins, losses, runs scored, and runs allowed against each opponent, I have divided each team’s runs scored and allowed into two groups: (1) games against these 6 “Bad” NL teams, and (2) games against all of the “Other” teams.
When I did this for the Brewers and Phillies for games through Friday, I find that the Brewers are averaging 5.62 runs per game against the Bad teams and 3.61 RPG against the Others. That’s a pretty significant difference of 2 runs per game.
The Phillies are averaging 5.78 RPG against the Bad teams and 4.19 RPG against the Others. That’s more than the Brewers in both categories, but over half a run more against the Other teams. The difference of 1.59 between the two groups is not as large as the Brewers 2.01.
Now here’s what I think is the most significant part of this. So far, in the Brewers 124 games, 55 of them (44%) have been against the Bad teams. The Phillies have only had 37 of their 126 games (29%) against these teams, an obvious reflection of being in a stronger division.
As an attempt to equalize the teams’ run production based on these different strengths of schedule, I adjusted the Brewers runs by (1) multiplying their RPG against the Bad teams by 29%, (2) multiplying their RPG against the Other teams by 71%, and (3) adding (1) and (2) together. That is meant to approximate what the Brewers run production might be if they played the same schedule as the Phillies. That exercise produces an adjusted RPG for the Brewers of 4.19, somewhat lower than their actual RPG of 4.50.
I don’t claim this to be a foolproof scientific method, but it illustrates my point. And the point is that the combination of (1) being more productive against the worst pitching teams in the league, which would be expected for every team, and (2) having significantly more games against those teams than other NL contenders, flattens out the difference between the quality of their offenses.
I have done comparisons between the Brewers and the other NL playoff contenders, and the results are all similar. The other contenders, except for the Padres, all have had significantly more productive offenses, especially when factoring in the schedules they have played.
Of course, the Cardinals come the closest to the Brewers in games played against these Bad teams. They are averaging 5.87 RPG in 53 games against the Bad teams and 4.14 RPG in 73 games against the Others. In addition to having a better offense overall than the Brewers, they are a half a run per game better against the Other (better) teams.