I've managed to pull it off against 3 people, but they were all white belts (like me) who I regularly submit.
I use it as 1 of 6 submissions from side control. I'm not so hot with terminology, but I think you'd call it a 6-lock flow.
3. straight armbar
4. leg americana
5. have no idea what its called, but you pinch your opponents far-side arm between your chin and shoulder (thumb against your neck), step over their head, grip your own hand around their elbow, and pull their elbow in the wrong direction.
6. Wizzer on their near side arm, step over head, bend elbow the wrong direction.
I'm terrible with these descriptions. We don't use terminology in class so I only know how to show someone else, not describe it.
The point is, it is a low-percentage move, but if it's one of six, you have that option depending on what your opponent is doing with their arms.
When I've caught someone with a leg-americana it was because they were focusing on avoiding one of the other 5 submissions in my list. I quickly (very quickly) refocus on their near-side arm and get the leg-americana.