Something's clearly not right with Hanson. He has an 8.79 ERA in his last three starts (15 runs and 21 hits in his last 7.1 IP), and an 8.31 ERA in day games (this one starts mid-afternoon). Sanchez is one of the more underrated pitchers in the league (7-4, 3.18 ERA), and he's fared well against Atlanta both this year and last.
Vegas was being lazy with this line, simply because of Atlanta's home record and Hanson's track record prior to his recent struggles. The Marlins are definitely a live dog at a great price here. Get it while you can, because it will only continue to get pounded down.