Did you feel along the leg from a break? That did look more worrisome than what I see when my Runners come up lame from a sprain, could be he has just been on it longer too trying to keep up with the other ducks. A really good examine feeling for any breaks. Any chance of a vet?
We all learn...
For now best is TLC. Having him in the crate makes him rest. Vitamins give him added boost. Maybe on a nice day he can have a visit by his girlfriends with you putting the crate outside?
Could be a sprain my Runners get them from time to time from running up and down the hill behind our home...