To get survivors down on the ground you'll need to hit them twice, which is certainly easier said than done. After you hit a survivor, your hunter will have a small but significant stall, where they stand still. This gives the survivor plenty of time to escape, and you'll have to give chase again. Remember they don't have to stand still for you to hit them, just get right up on their back while chasing, and watch for any traps they leave in their wake.