As for catching and handling, any treatment is best done as the sun sets and the chickens roost. This way, they will be calmer and struggle a bit less.
MrsB
It looks like this could be scaly leg mites (barring injury or pecking).
If it's mites, you'll have to treat the whole flock, change the bedding out, and Sevin dust three times, seven days apart to kill any mites or eggs in the coop.
Go with me on this:
Day 1: Dip legs in gasoline... DIP...