Sounds to me like someone.... maybe the kid, or maybe some other miscreant, deliberately set an IED with a pressure switch, or if it was the kid, things went wrong, and he tried to step on it to stop the fuse but not quite quick enough. 

It really doesn't take a lot of explosive to detach body parts.
 
Most pressure sensitive explosives require much more than the pressure of someone's weight to detonate.  So I think the fuse was lit by the kid and he was trying to put it out or someone was just being evil by leaving an IED for some poor soul to step on by mistake.

the proper name for this is "Land Mine"

I know how to make M-80s but I don't do it because I ALWAYS think bigger and more is better and I surely would end up with an M-360. I think one of those cardboard coin tubes the banks sometimes use would work nicelyThen I'd probably blow a crater into the drainage "pond" (which is always dry) across the street, break some neighbor's windows or something. It's always more fun thinking about things like this than actually doing them, unless of course you're still under 20yo and still immortal and untouchable.
I saw a video yesterday of some guy with a fountain sort of firework, like maybe a foot long, about 4" across at the base and tapered to a point where sparks and fire shoot out of the end that. It looked like a "Hey y'all, watch this" moment. He had his jeans unzipped and unbuttoned and the base stuck in where the zipper is. It all went well, fire and sparks shooting out like he planned until he started his "moves"... then the thing slipped down but stayed in place except it was now pointed up toward his face. It didn't take too long for him to get it out and begin slithering around on the ground like the human snake, lol. It didn't look like he got injured, more like a close call but still... light the fuse and move away. I've seen M-80s blow a mailbox to pieces, saw one blow a metal 3 gallon bucket into small pieces. They would put up a 20' mushroom cloud, they were GREAT toys for kids! I miss cherry bombs too, they would sink when thrown in water (lake) and make a big flash under water. I think people used to fish with dynamite, probably with M-80s too.
I loved playing with M-80s but I never tried to throw one, even I was smarter than that.
 
That thing in the park, who knows. People are a lot meaner and more likely to hurt someone for fun these days. Some things I don't understand. Violence for fun is beyond my ken.
 
J

Well now the cops are saying the device was pressure sensitive and was probably left by some "explosive enthusiast." 

So the PC term for a friggin eedjit is "explosives enthusiast", good to know.

This sounds like a really good case for the principle of "reaping and sowing", "what goes around, comes around", or "karma" as you will, to start working on. What a bad deed.
Why.. what sort of person would do that? What makes people capable of such things? I can comprehend a criminal, some highwaymen robbing for money or something like that but I cannot comprehend something like this. What sort of person can do things like this and live with it? There is no gain from it, just pointless misery. I don't get it. Maybe I'm glad I don't get it.
J