1. What is my best response if I see somebody being harassed and the runner is aware of it?
2. What is the best response if the runner is unaware of the person lurking/leering at said runner?
Thank you for asking.
1. Intervene any way you can, but the best would be to walk up and ask her if she needs help. "Hi, do you need any help here?" If the harasser left before you could get there, same thing holds. "I saw what happened, do you need any help?"
2. This is much trickier because she doesn't know your intention, regardless of what you say. I would suggest to wave or call from a distance so she knows you're approaching, give her a good 5-10 feet of space, tell her what you saw, and ask if needs help. "I'm sorry to interrupt you, but I saw ____ and am worried for your safety. Is there anything you'd like me to do?" Helping could mean confronting the creep, running with her, ahead/behind her, waiting at the parking lot, etc. This is a weird/scary situation, so give her a minute to weigh options. If she declines, tell her your name and what direction you're going so she knows if she'll run into you again.
I'm especially curious what other women think RE: point 2.