Andrew Keegan BANNED From L.A. Bar Over Drunk Skateboard Attack ... Says Lawsuit

Pretty boy Andrew Keegan has been BANNED FOR LIFE from a fancy L.A. bar/restaurant after drunkenly attacking a bouncer outside ... then ramming the guy with his motorized skateboard -- this according to new legal docs.

TMZ broke the story ... Keegan sued James' Beach restaurant in Venice, CA back in November, claiming several bouncers beat him up in 2010 for no reason ... while he was minding his own business on the street.

But the bouncers are now telling a much different story, seeking to countersue Keegan for assault and battery -- claiming the former '90s child star attacked them first ... all because they refused to grant him entry into the restaurant.

The bouncers claim Keegan was visibly drunk/high and could barely stand -- and when they told him to buzz off, he flipped out ... pushing and battering the bouncers, then ramming one bouncer in the shins with his motorized skateboard.

According to the docs, filed by attorney David Diamond, the owner of James' Beach then informed Keegan he was banned for life.

Keegan allegedly continued his assault until the cops arrived ... and then took off on his board ... only to return minutes later. The bouncers claim they had to call cops a SECOND time to get rid of Keegan for good.