In American Football, if you do not insert your mouth guard is it a foul/penalty?

I remember the refs would make us put it in in High School, but I can’t remember if it was a penalty. I don’t think anyone really cares in College or the NFL.

no its not a penalty

in most states high school players are required to wear mouth guards . NCAA and NFL dont have a rule requiring them.

Yes it is a penalty. It is even a penalty if you are wearing it wrong, like only having half of it in your mouth. 5 yard penalty in College and High School.