I remember back in the 2008 MLB season, I went over 65% on over a hundred bets. A large part of the system was fairly simple. Whenever both pitchers in a game were on a roll with great numbers in their last three outings, I played the under. Many of the lines were in the 8-8.5 range, and maybe a rare 7-7.5 when two dominant aces faced off against each other.
The following season, the books adjusted accordingly, and I broke even before realizing the edge had gone. Many of the lines felt like they had shifted down about half a point. In the last couple of years especially, it's felt like more and more lines in the 6-7.5 range have been sent out when aces faced each other.
Pretty much the exact same play as SF@BAL three weeks ago. To me, this bet feels much like those 2008 baseball bets. Two dominant defenses (1st and 2nd in PPG) are going against each other, with San Francisco giving up 14 ppg and Pittsburgh giving up 15.2 ppg. The 38.5 line is just like those 8-8.5 lines I used to get in 2008. I really believe that the proper line when two dominant defenses like these play each other should be in the low to mid 30s. Perhaps we all need to get in on this before the books make adjustments next year.