It is kinda complicated. I figure total runs per team by going on the average stats on this year. Comparing each pitcher's era to the opponent's obp along with their slugging avg. I do this to try to get a feel of how many runners are probable to get on base, and from there figure the probability of them producing runs. I also keep in mind elements like weather, pitchers comiing of the dl, and soforth. Granted, things happen such as unexpected weather, wind, stadium, or just plain shitty days either pitching or hitting. Therefore, it isn't foolproof, but then again nothing is. It takes alot of time to figure all games everyday, but right now I am not so busy. Usually it is pretty accurate if I stick with the strong plays. I only play if it is a strong play, I don't mess with anything that is close.
hope this could help,
HookEm