Justin has 12 RBIs because the hitters in front of him (BUpton/Heyward for the most part) have been ice cold. Certainly doesn't help your cause when you're hitting after the pitcher and two guys with a combined .275 OBP in front of you.
This explanation is superseded by what Upton does
when runners are on base, as JS22 pointed out. Especially when we compare him to the player who now occupies his #5 spot in the D'backs batting order, Goldy.
JS22 said:
Justin some interesting numbers...
Runners on Base: .222
Runners in Scoring Position: .250
Bases Empty: .429
Now, Goldschmidt:
Runners on Base: .476
Runners in Scoring Position: .400
Bases Empty: .240
Polar opposites.
As I alluded to with reference to Curt Schilling, pitchers challenge sluggers to hit their best pitch when the consequence would be only a solo HR. They are a lot trickier when runners are on base.
Hence, Upton's strong HR start with the Braves. He has evidently been coming up more with the bases empty or not in scoring position because of the two guys hitting in front of him, including his brother. So he is hitting solo shots as the pitchers work their way into full-season form.
Runners on Base: .222
Runners in Scoring Position: .250
Bases Empty: .429
'Same problem we had with him in Phoenix. He hit more like a leadoff hitter while batting 3rd, then 5th, for us all of last season. He is consistent!