Re: Static Stretching...
You can easily get injured just by moving your body through a range of motion... Particulary as uke... With the odd positions we're in, gravity and our own body weight provides plenty of force on the body.
You tenkan quickly but your foot doesn't quite keep up and you put a funny torque on your knee.
You squat low in a horsestance
You knee walk, which puts all kinds of weird strains on all kinds of parts of your body
E.g., someone does a technique on you that raises your shoulder to a point where you'd normally be perfectly fine but one day you're a bit stiffer and suddenly that was too much or too sudden.
You lose balance, stumble to regain it, and twist an ankle or knee.
You are thrown and get up oddly, putting a lot of strain on something in your leg.
You're thrown a bit differently from normal and have to suddenly twist your whole body in the air to land safely.
You land funny and your back muscles take the impact, or a shoulder.
Tendons, ligaments, muscles, all going through a big range of unusual motions.
I find warmups before help (by which I mean things that actually get you warm, not static stretching), and I find stretching AFTER helps a lot, and generally being flexible and strong helps prevent injuries.