i have had the same problem with knee braces. Player is warmingnup with a brace with a hard plastic hinge.
Because it was a JV game I didn't notice the brace (player had pants). With 3 minutes I go to the coach and tell her that player 32 has an illegal brace and she can not play with it on.
Coach says classic she has played with it all year and no one has said anything. I told the coach that normally a brace like that one comes with a cover.
At this point the head coach and AD come over. I explain that the brace is illegal. I asked if they agreed that the brace had exposed hard plastic (not the smartest way to handle it). They did agree it was illegal.
The AD yelled at the girl and asked if there was a "cover for the brace"? The girl said yes and it was at home . The AD said he would get the parents to go get it.
The coaches wanted to know if she could play with the brace until the parents came back with the cover. I asked them again if they agreed that the brace was illegal. They did. So we started the game with out the player.
A couple of lessons, even in a sub varsity- check uniforms and equipment as early as possible so that the team can adjust and or find the proper equipment.
Also do your job enforcing the rules from the start of the season. In this case this the player was a freshman playing in a soph game. Freshman officials are normally "newer" but this brace was obviously illegal.