Ya gotta see the video from Drizzy's Friday concert in San Francisco ... he's onstage talking to fans between a break in songs when suddenly a book comes hurtling out of the crowd, and he snatches it with one hand.

While it appears the book may have gone over his head, Drake told the book-thrower ... "You lucky I'm quick. Would've had to beat your ass if that hit me in the face."

Champagne Papi's been totally cool with women throwing bras at him during his concerts, even helping one big-chested fan go viral and land modeling deals.

But, it appears book throwing is crossing a line for Drake.

It's part of a larger trend unfolding at concerts ... Bebe Rexha got hit in the face with a flying phone, Keslea Ballerini took a friendship bracelet to the noggin and someone even threw a bag of cremated ashes at Pink.