I followed everything it says here for my Ball Trapper (Catcher).

1. Create a env_sprite entity, set its Sprite Name to "sprites/physring1.vmt", set its Parent to "ball_trap" and Name it "ball_trap_sprite". Make sure to have 'Render mode' set to Additive. Also, the 'Scale should be set to 1.5 'Size of Glow proxy' set to 0, and HDR Color Scale set to 1.0, yet all these values can be changed to your liking. Also be sure to have 'Render Fx' set to Distort.

Umm.

When I did the trigger, I set the sprite to show up.
It didn't show up.

What's wrong?

Did you make the material yourself? If so, did you make sure to set the alpha channel correctly? (black = showing, white = not showing)