We have a kid in church, nice enough now, who when he was little would run around, never settle down, disrupt things- and was generally thought to have ADHD except that whenever a male authority figure would tell him to sit down, be quiet & stay put- miracle of miracles, the ADHD vanished!
I muttered once to the agreement of all who heard me- “It’s not A-D-D- it’s the absence of D-A-D.”
As it turns out, my parents did scold me for what I did to the cats. Our cats were not big fans of being chased around the house. But apart from the psychological damage inflicted, they lived to ripe old ages, so that’s alright.
Touche.
It sounds like the kid in the OP is bored off his rocker, not necessarily hyperactive. Better he entertain himself outside than in; he’d probably break something with all that energy. Even if the grandparents watch him regularly, they probably don’t have all the toys the parents do, so he’s got to do something to entertain himself.
My son does the same thing when he’s bored and he’s got a room full of toys. As soon as he starts trying to do stuff like that inside, we send him outside to do it someplace more appropriate. And if you take away the sword, he’ll use a stick. As long as he doesn’t harm animals, people (himself and others included) or landscaping, I’ve got no problem with it.
I never doubted that ADHD exists since despite the strict supervision of one or two of my parents whenever I was in public, and frequent discipline including lots of yelling, spanking, slapping etc - I never stopped moving when I was a kid and was constantly doing inappropriate things and pissing off other people. Some kids can’t control themselves enough to be socially acceptable and other people have a hard time controlling them as well despite their best efforts.
Running around beating hedges with a stick/fake sword, though - totally normal behavior for any 6-year-old. As is brandishing it at cats IMO, it’s only over the line if they hit the animal.
I spent my childhood using a real weapon – a .410, sometimes called a rabbit gun – but if I had randomly killed animals or terrorized animals, my mother would have had my hide. Attacking the bushes, normal behavior. Cruelty to animals, not so much.
I’ve no doubt that if he’d had the control to wait for the cat to approach him, he’d have whacked that cat senseless. 
You’re reminding me of our neighbours across the street, ivan. I think their young son (around three or four) is normal enough, but when he’s out, he’s screeching. Unfortunately, their rental unit only has a front yard, so when he’s out screeching and I’m trying to work in my front yard, I have to have my iPod on to block out the never-ending screeching. That’s annoying, but where it gets weird is that they don’t seem to have a problem with him playing on the sidewalk of a very busy road where people drive much faster than the speed limit. I really don’t want to look up from weeding my front plant bed to watch a youngster get run over on the street.
ETA: Forgot to say that they have a completely enclosed yard; there’s no reason for the young Master to be playing right next to traffic.
As for hitting hedges, kids can hit their own hedges all they want. If they start hitting mine, though, we’re gonna have a problem.
By the breadth of a sword blade, this seems better suited to MPSIMS.
Wait, this is normal 6-year old behavior?
I’m 20 and I still pretend to swordfight with sticks!
You seem to be assuming that there’s a difference between a normal 20-year-old male’s behavior and a normal 6-year-old male’s behavior. Assuming facts not in evidence.