You are the Game Master. In the middle of a fight, one of your PCs pulls a handful of sand out of his pocket and throws it at the enemy's eyes. Yes this PC was previously established as having sand in his pocket.

Quick, without looking anything up, adjudicate this action in the manner you believe is most in line with your preferred system's rules.

After you answer you may look it up. Did you get it right? I bet you didn't.