Most "glasses" use a polycarbonate lens these days which is pretty good at resisting BB's or lead pellets. Unlike glass it won't shatter on impact. Polycarb lenses are lighter than glass and so long as they are anti-reflective and scratch resistant coated they work well for shooting. Industrial safety specs will have (probably) side guards to help prevent debris flying into you from the side, you could easily tape over one lens to form a blinder but you will have to check the competition regulations to make sure your blinder isn't oversize.