Gravity. Doesnt make alot of sense the way its themed now, but mechanic wise it seems sort of like a reverse gravity shield.
Repulsion shield?
It does absolutely make sense. If you barely touch glass - nothing happens. But if you throw a rock at high speed at the glass, it will probably break.
An element shouldn't have a shield and the opposite as you're stating. But Gravity isn't a bad idea.
Repulsion shield sounds good. I'll stick with Glass though.