I've always been the careful type. Always plotting my course, making sure there was ground past the jump before I would do it. You know, common sense stuff.  But something happened to me the other day that will probably have me out of comission for a week.
I was doing a turn vault on what looked like a sturdy wall. As soon as I cleared it and my feet hit the other side of the brick wall, the whole top part of the wall came down in one big chunk on me. As soon as I landed on my ass, the huge chunk of concrete and brick(must of weighed at least 60 lbs) slammed down on my right knee, smashing my leg into the ground at the same time.  It hit with so much force that the piece of brick wall shattered into smaller pieces. I was in so much pain I thought I broke my leg. After all was said and done, there was just swelling and heavy bruising. Needless to say, from now on when I'm doing a slow run through my course, I'm gonna test the strength and stability of any wall that looks even remotely shady.  Even tho I would hate to destroy public property (gives us all a bad name), I'd rather give a wall a few kicks and have it come down than go through what I'm going through right now, or worse.  All I gotta say is thank God the fall was only a few feet, otherwise it would have been ALOT worse.  Hope this info keeps a few of you from getting hurt.

that is terrible.

Spotting and testing terrain is def. a big part of parkour.  Hope you don't have to stay down too long.

almost the same thing happened to my cousin, did a wall run, and the top of the wall came off....bad news.  good luck on your recovery.

wow man thats too bad, good luck w/ your recovery.  Thats on of  those things that bites you in the ass after your sure youve completely checked an obstacle.
as a rock climber, I have experience with checking my surfaces for stability, your story was a good reminder for me to keep doing that.

Thanks for the replies guys. Glad this could serve as a reminder. I never really thought of doing it because nothing like this has ever happened to me before and it was a double stacked brick wall. I just wanted to pass it on just incase there was anybody else out there that it had never occured to also. My knee's still all fucked up. I was tempted to go to the doctor to get an x-ray because it's hurting a little deeper than the bruising, I think it might be the bone (hairline fracture possibly?), but I'm broke so I dont have enough money to pay for the checkup or subsequent medical treatment. I'm just giving it time to heal while eating a crapload of vitamin d and calcium. 
Digital Kid

yeah, look before you leap. i was going to do a lazy vault over a rail yesterday in cross country. i had my hands on the rail, then i noticed about 30 feet of air before thorn bushes. to think that i was just a small muscle twitch away from probable death/broken legs is something of a horrifying thought.

applauded  Good way to put it.

i should start doing that...