I've been playing against more opponents that are not getting knocked down in arena. With my spinning slash I see them get knocked back when I hit them with the follow up from spinning slash they take the hit and are still standing. Gladiators rely on trying to put someone down on the ground so we can connect with our ground bash and scars of dust.

There is no hack. Knock down doesnt always hit. Some skills are 100% chance and even those skills if you use it on another class while theyre in the process of using another skill it won't stick, some skills will.

Learn your class, and others