here's report so far (see update below). Lester seems to be feeling better now with bruised ribs and more. His Facebook page here with condolences and photo of damage. Picture of him back then and now at left.
Sadly he had just started a comeback (he's long claimed he was screwed over for royalties) aided by musician support groups and Kickstarter. Lester goes all the way back to mid-'60s, when the group appeared with Joan Baez at Newport. The 11-minute "Time Has Come Today" appeared in numerous movie soundtracks, most famously (in its entirety, or so it seemed) at climax of Coming Home. Appeared with John Lennon when John co-hosted Mike Douglas Show during a famous week in the '70s. And so on.
UPDATE: First mainstream account here. Woman, 43, arrested and charged with battery. Chambers' family firmly believes it was racial incident. Video has now surfaced of the actual attack, at very close of video: