Bussing

From SA Mafia Wiki

Bussing is when a member of the Mafia votes for one of their own in order to distance themselves from the scum and gain credibility with the town.

This is the kind of move that can backfire on you pretty hard if you're too obvious about it. Likewise losing a member of the scumteam can unbalance the game in favor of the town, so typically mafia don't bus each other wantonly.