The sacrifice being the hair from their body. The swimmer sacrifice is when a male swimmer has to shave his body for an important meet, though it usually is used to refer to when a male swimmer shaves his arms and legs.
Samuel: So that's when I did the lion king to her.
Richard: Holy Shit, what did she think?
Samuel: She was totally fine with it! She laughed!
-They both look over to see another guy with hairless legs-
Richard: What the fuck? Why did he shave his legs? What is he gay?
Samuel: No he's just a swimmer. The swim team has their championship meet tonight. They all shaved down.
Richard: Is it that important?
Samuel: Anything you can do to cut down on drag you do. Its the swimmers sacrifice that every male swimmer must do.