The Knocked Up star found himself in the middle of the birthing drama and watched on as the new mum was loaded into an ambulance by emergency workers.
Hill later took a picture of the scene - but was left red faced when a TMZ.com photographer caught him.
In a post on his Twitter.com page, he writes, "Craziest thing I've ever seen. A woman have (gave) birth next to me in a park. I took a picture of the placenta and TMZ caught me. Embarrassing."
