Just had it happen about 1 week ago with my 70-200vr, mounted it and was trying to get the foot in the tripod and wiggled it next thing I know my lens hit the floor

( off course it was a concrete floor no carpet in that church, Im not sure how it happend Ive been switching len's for over 20 years and never a drop, Altho in Oct I dropped my D2hs with this same lens
when carrying it by the tripod mount I didnt realize there was a quick lock button I depressed and dropped both of them, camera took the brunt and cost $200 to fix, this one is on its way to Nikon for estimate, it smashed the mount & some of the electrical contacts no glass that I could see