Seagal's fighting skills are outstanding. He's an accomplished martial artist. The stuff he did in "Above The Law" would work in the real world, if you had the strength and speed. Of course in the bar fight they wouldn't have fought him one at a time.
That big bald guy in that bar scene is Frank Degeberg from the Degeberg Academy in Chicago. He's a real character and cross-trained in a number of different martial arts. He would be hard for Segal to beat in a real bar fight.
Another notable martial artist that Segal faced in another one of his bar fight scenes was Dan Inosanto, 'sticks'. I'd put him in the unbeatable category for Segal, or almost anyone else in the world in a real 'stick fight'.