There were 15 runs scored when the Rockies and Diamondbacks played Wednesday. Forget that. Different pitchers and different circumstances today. Both factors should have a huge influence on this game going Under the total. 
The roof was open at Chase Field on Wednesday. It also was open on Tuesday when the teams combined for nine runs. But today the roof is going to be closed because of an earlier than normal starting time, which will be mid-afternoon local time compared to the evening. Chase Field becomes far more of a pitcher's park when the roof is closed. 
The pitching matchup is lefty Kyle Freeland versus Zac Gallen. All Freeland does is pitch in games that go Under. All Gallen does is continue to impress in his bid to be a staff ace and elite pitcher. 
Freeland has a 2.87 ERA. He pitches deep into games, too, going at least six innings in all six of his starts this season giving up no more than three runs in any of those outings. The Under is 12-3-1 during Freeland's past 16 starts, including 5-1 to the Under this year. 
Before scoring seven runs on Wednesday, Arizona had been held to an average of 1.7 runs in its last eight games. The Diamondbacks' offense has been far more effective going against righthanders rather than southpaws. 
Gallen has a 2.25 ERA in six starts. He has allowed three or fewer runs in each of his first 22 big league starts. This is a record he currently shares with Aaron Sele, who did it with the Red Sox. Gallen can break the record today. Gallen holds a 2.27 career mark at Chase Field holding foes there to a .187 batting average with 56 strikeouts in 47 2/3 innings. 
The Rockies are a far less dangerous hitting team away from Coors Field.