I like playing 2nd half unders in games where there were a lot of turnovers resulting in points, runbacks etc during the 1st half. It can take a defense a half to settle in. If the game is low scoring to begin with, you can sometimes get a high 2nd half line. You need to look at the total neutral and unbiased. If a 2nd half line is 16.5 and they scored 20 1st half, you lean under. The over looks easy to someone not closely watching the game. Sides are tricky, sometimes capped to prevent a middle/hedge etc.