Sublime's summer tour nearly came to a screeching halt last weekend -- when the band's bassist dislocated his shoulder during a freak longboard accident ... and his rottweiler's to blame.

It all went down Sunday at Summerfest in Milwaukee -- sources close to the band tell TMZ, Eric Wilson's rott was pulling him around backstage on his longboard ... when the bassist took a nasty spill.

We're told Wilson's hand had somehow gotten tangled in his dog's leash -- and the strong animal dragged him 10 feet, dislocating his right shoulder.

Paramedics responded to the scene and rushed Wilson to a nearby hospital, where doctors popped the shoulder back into its socket. Eric's now back on the road, but still recovering.

Lucky for Eric, he didn't injure his left shoulder, which supports his bass strap and does most of the moving when he plays. Eric's rep tells us, "If he had injured his left shoulder, we would have had to cancel the rest of the tour."

Feel the break, feeeeeeeel the break.

One of the founding members of Sublime has quit the band ... again.

Moments before Sublime with Rome took the stage at The KROQ Almost Acoustic Christmas concert in L.A. this weekend, drummer Bud Gaugh announced the show would be his last.

When asked why he was leaving, Gaugh said, "It's a long story" ... adding, "The story is that I'm gonna be a dad here again real soon, and I just wanna be there for my family."

But the tension had been building for a while -- TMZ broke the story, Gaugh stormed off the stage at a concert last month after hurling cuss words at the band's manager, Mike "Cheez" Brown.

We're told the guys tried to bury the hatchet ... but it seems things finally reached a breaking point.