30 Days of Wincest ╬ Day 26 - Favorite Sam Protecting Dean Moment

Season 4 episode 16 - On the Head of the Pin

Something happened to him downstairs. He’s not who he used to be, he’s not strong enough. […] You think I wanna do this? This is the last thing I-… But I need to be strong enough.

There are multiple levels of Sam protecting Dean with this scene. He pins Alastair to the wall to keep him from killing everyone, he “interrogates” him so Dean doesn’t have to anymore, and then, with a noticeable level of satisfaction, he kills the demon who personally tortured and broke his brother for 4 decades.