Definitions for "Backside wall"
When standing at the top of the halfpipe and looking down towards the bottom, the backside wall is the left wall for regular footers and the right wall for goofy footers. If you ride straight down the center of the halfpipe, your backside wall is behind
The halfpipe wall behind the rider. This varies between regular and goofy-foot snowboarder.
If you ride straight down the pipe the backside wall is the wall that your back faces.