How can i teach my dog to chase people?

how do you teach a dog to *fetch* somebody without harming them i had a dog once that was trained to walk without a leash and if someone ran we held him then told him to chase and let go he would run up to the person and nip at there heels his previous owner taught him that and im wondering if i can get my dog to do the same thing but instead of nipping at them grab them and pull them back to me (i don't have to worry about people getting hurt my dog will latch onto your clothes but when he's dealing with flesh he's amazingly gentle even when he's exited)