I had a really big guy just drop all his weight on my legs/knees while I was holding closed guard to open my guard. It worked he opened my closed guard and all 285 pounds ripped my groin. I'm 190 pounds. I still don't really know how he did it just kind of hopped up then came down on my knees making me do the splits. I don't work closed guard on big guys anymore. It's all knee shield and butterfly guards if they get me on my back. I try to move around them as much as I can.