User blog comment:IceFireWarden0/Warden's Thoughts: On Jaune Arc and His Weaponry/@comment-3286116-20140301194214/@comment-3146930-20140301214452

Yup, when Cardin punches Jaune and there is that big flash of light (causing Cardin to hurt his hand), there appears to be some kind of force field around him. During the commentary, they mention that this is a hint to his true Semblance. I think it is short-term invulnerability, but I could be wrong.