Mine: Overhead Squats.
Root Cause: Flexibility & mobility limitations
I've pretty much been a "stiff" my whole life. I've never had even above-average flexibility or mobility. Mostly, I think, because I didn't ever work on it. At least I waited until my late 30's to wakeup to this! The impact of the issue, for me at least, is evident in many areas of my life including Crossfit movements, Krav Maga (nearly everything we do), and even recreational stuff like scuba diving ie(reaching back for my valves).
Krav Maga 1
Inside defense & round kick until we all died :)
More round kicks...weee...heh