I am not sure what can be done about the broken leg, if anything. Do you know what kind of frog it is that you stepped on. Depending on what the species is determines how the enclosure should be set up. By rule of thumb though, sick or injured frogs should be kept in a hospital tank. A hospital tank is a striped down version of what you would normally hose the frog in and the bottom of the tank should be lined with white paper towels. For example; if it is a tree frog you would give him a small bowl of water to soak in (spring water, no matter what species, to avoid heavy metals and chlorine),a plant to climb and hide in unless he is too injured to climb and maybe a branch to sit on. If he is a water frog, he will need a larger bowl of water to soak in and something for him to hide in as well like a butter bowl turned on it's side and cut in half to make a cave. The purpose of the white paper towel is so you can monitor the frogs dropping for changes and also keep track of blood loss as well to prevent infection due to exposure to the substrait and other things in a regular tank. Since you think the frog has a broken leg, you will want to limit his mobility.Don't put him an excessively large enclosure. Basically, just make sure he does not have to move around much to get to the things he wants; the water and hiding place. I don't think having him on the porch is a good idea. He may get over heated or a neighbors pet may get to him also. If you think he needs the light, bring him in and put his tank near a window, but make sure only half of his tank is in the sun, he needs to be able to get out of the light and heat if he wants to. Frogs are very resilient little creatures and bounce back quickly with good care. Depending on how bad the break is on his leg though, you may not be able to release him back to the wild after the break heals. It just depends on if the injured leg is a front leg or a back leg and how well he recovers. If it is a front leg, you may have a pet for the rest of his natural life. Also if the little guy has and open wounds near the break, you can apply Neosporine with a cotton swab to help it heal. Just make sure it IS NOT the kind with pain relief as that will kill the little guy. The pain relief kind is used to humanly euthanize frogs so it is very important that you have the correct stuff! I hope that I have give you at least a good start on how to care for the little guy. Good luck to you both and if you have any other question, please feel free to ask. There are a lot of well informed people here on the forum and we would all be happy to help if we can.