Pummeled to the Ground
On Vancouver Sidewalk
It's unclear exactly what provoked the attack -- but we're told Shia originally got into it with the man inside a bar called Cinema Public House ... and after security kicked them both out, the man tore off his shirt and unleashed the fury all over Shia's face.
Moments after the attack, Shia tries to chase after the guy -- but someone who appears to be his friend holds him back, telling him, "You gotta lay low right now!"
A rep for Cinema Public House tells TMZ, no one on staff noticed the brawl outside -- but the rep confirms ... Shia has been a regular at the place since he's been in town to shoot "The Company You Keep."