Whitebelts, uneducated Gracie Barra cult members, gather round. Where did we get our name from? Well, an illegal move. It's not a submission, but it can lead to some nasty heel hooks and some blown ACL's.
The IBJJF rulebook defines knee-reaping as “when one of the athletes places his thigh behind the leg of his opponent and passes his calf on top of the opponent’s body above the knee, placing his foot beyond the vertical midline of the opponent’s body and applying pressure on his opponents knee from the outside, true inside, while keeping the foot of the leg at risk stuck between his hip and armpit.”
Here's a picture I stole from the internet to show you
It's not a nice position to be stuck in, but there are plenty of BJJ positions that are awful to be stuck in too. Ever been crossfaced? It's not nice. The key difference is the timing of the tap.
If someone catches a heel hook, before you actually feel enough pain to warrant a tap, it's too late. You're either okay, or your knee's completely blown out. Which is why so many competitions make it illegal and many gyms won't teach lower belts heel hooks. Should they? In my opinion,
yes. The sooner you can make your students aware of it, they can learn the dangers of it, learn the escapes, counters and how to ultimately avoid losing their knee.
Many academies teach a 'catch and release' system with heel hooks. You both know you don't need to crank it on, if you've got it, you've got it. Even if they don't tap, just let go.
Yes accidents happen, but they do with all submissions, I've had my arm broken and been choked unconscious, simple mistakes usually led by (my) ego.
That's where we got our name from, to keep it illegal would actually make us continually seem cooler, but, we want to set the Reap free.