In a new basement room, our light switch has been working fine until today when a shower of sparks erupted when my husband turned it on. The room is not finished yet, so there is no switch cover on. We can see that at the point where one of the black wires is wrapped around the switch contact, the screw is blackened/scorched. Is it possible that the ground wire came into contact with the load wire and caused the sparks? What else could have happened, and what should we do to make sure this doesn't happen again?

Thanks in advance for your help!