Basically, about 20 years ago the skaters used to ride in all day and night, people complained, so the council cut the rail and put a grind stopper and bolted it so a bigger bit was sticking up on top, someones undone it, broken the weld and spun it round so that it's grindable just a bit sketchy till you get used to it. Would take it off but the pipes cut underneath it, will probably file it down gradually though man