At around 8:30 this morning, the hydrant at Sanchez and Day in Noe Valley was knocked over, creating this glorious/frustrating scene. SFist reader and local photog David Gallagher captured the watery explosion, noting, "San Francisco Fire Department works to turn off valve to knocked over fire hydrant."
We're not sure how the hydrant came off, exactly, but we'll update as soon as we know more.