Hobbit on Quest (he/him)
Well, you can, but I don’t think that’s why Matt does it. Notice, he doesn’t do it for every opponent dropped or just for melee attacks. It’s the signal that this ends the fight and so releases all the tension and, naturally, brings out the cheers at the table (and among the viewers). So, it is good GMing, but not because it fits a 5e rule.Because by 5e rules, you can either kill or knock out your opponent. The GM asking is good GMing.