I agree that fuckery is the most likely explanation in this case. However, ricochets do not need to remain at a constant height or velocity to hurt someone. A round bounced backward and arched just enough to clear the treeline would be enough. I'm kinda shocked an outdoor range would be allowed this close to those fields. Regardless of physical danger, imagine concentrating on playing ball while gunshots ring out in an adjacent lot!

My point is not that heavy volume is required for this to happen, and it's strange how you could jump to that conclusion.

Instead, a higher rate of fire gives more opportunities to witness anomolies between shots, within a given time. Combine this with tracers, and now you can easily follow these paths, before and after each bullet hits it's initial target.

With a 6000 round-per-minute minigun, even if you only see one tracer bounce away every second, that demonstrates a 1% chance for every round to deflect and hit somewhere unintended.

Considering that the tracers are normally spaced out on a belt, with other rounds between them; the sample size can be reduced further, and this chance becomes multiple times higher.

When yearly machine-gun shoots were still hosted in Knob Creek, Kentucky, the range staffed people left and right of the firing line with fire extinguishers. After the 'finale' occurred and weapons were cleared, they would run out onto the hills beside the range.

With multiple miniguns firing alongside other automatics, and the insane number of rounds fired downrange, it was inevitable to have more than enough hot tracers land in the brush of these hills to start multiple small fires.

The possibility of ricochet injury is simply matter of probability. Sure, I would never claim this is the most probable explanation, but it's silly to claim there's absolutely no chance this could happen.

If you've seen tracer fire in real life, I doubt you would keep that position. The fact that a falling bullet traveling at terminal velocity is enough to kill or injure someone, combined with the fact that bullets travel for miles would instantly tell you otherwise. Watch tracers fired at night and you can see how frequent ricochets are when hitting a mix of rocks in dirt. The last video I shared already demonstrated that complete trajectory reversals are even possible, not that this is even required in this circumstance.

The baseball field is only about 1/2 mile from the range backstop (about 22% of a 5.56 bullet's maximum range). All it would take is a rock plowed up into an inopportune position on the berm to set off a freak accident. Now, as I've said in another comment, I absolutely don't believe this is the most likely explanation; however, to discount it as an impossibility is ignorant.