August team ERA
#1-4: .500 or above
#5: under .500 (Giants: 6-13)
#6-19: .500 or above
#20-30: under .500
The reason for the Giants problems is, of course, that they have scored the fewest runs of any team in August. They were 4 games in front of the division in late July and now they're down by 2.5 games. They have blown a golden opportunity to gain ground by losing their last two games against the Astros while the D-Backs have lost 4 in a row.
It seems clear what the division will come down to in the final month: The Giants will pitch very well. The D-Backs will play solid ball but probably won't be spectacular in any particular area. If the Giants continue to hit like this, they will not make the playoffs. If they can hit a little better (though still pretty bad, like 22nd as opposed to 30th), they might be able to eek it out.
They've done it before (they were 25th in runs scored in July), so this will be what we need to watch in the coming weeks. If the D-Backs can get back to playing decent baseball and the Giants don't start hitting soon, they could be out of it in a few weeks.