I answered on your other thread, https://www.backyardchickens.com/th...uck-on-his-bottom-help.1192766/#post-18859925
but make sure there are no maggots present, since this looks like it could be flystrike. Here is some information to see if that is what you are seeing:
http://www.the-chicken-chick.com/2014/07/flystrike-in-backyard-chickens-causes.html
It looks like @Eggcessive has given you excellent care tips, advice and links on your other thread. I agree very much this looks like FlyStrike.