wondering what was wrong with my chicken

[gameboygal12]

I had this young barred rock chicken named vulture. he seemed to be a runt. but he was pretty much fine until one day, i went to feed him and he was literally "sitting" on his butt! he looked like a penguin. and when he walked, he really looked like a penguin waddling. and i would try to get him to stand and he would fall and sit on his butt again. so I would separate him from the rest of the chickens and give him a bowl of chick food. then I came back a few hours later and he was walking normally. then a few days later, he would do it again! then get better. does anyone know what was wrong with him?
this is what he looks like:

 

[dawg53]

Have you checked to see if your chicken has poopy butt? Scaly leg mites? Lice or mites around the vent area? What does the poop look like? A thorough inspection would help.

 

[gameboygal12]

I don't have him anymore, all this happened about a year ago. I gave him away to one of my friends and he seemed to be fine once he grew up. but I was just wondering what was wrong with him. his bottom was clean, his legs were fine. but his feet were kinda big. I think he must have just been a sickly runt. he came with a few chicks that i ordered from Mcmurry hatchery just to warm the main chicks that I ordered.