Backlighting. The sun behind the subject, so that the head is outlined by bright light and separates from the background. But then the face is often dark. It is a delicate balancing act with which I have had little experience.
Near the Selby Library in Sarasota, I had a good chance. A portion of sidewalk was under roof and fairly dark. A woman quickly walked my way, and the sun behind the left side really lit up her hair. I intercepted her and asked my question, even though she was clearly in a hurry. Kelley agreed and seemed both shy and flattered. I quickly clicked away.
Of course, I am a bit frustrated by the result. The light in her eyes is good, and I like the relaxed expression. But Kelley's hair is clearly blown out (overexposed) on her left side. Backlighting. Can't have it all!