By Ken Tucker
Updated September 24, 1993 at 04:00 AM EDT

Pity the star of the Sinbad show (Fox, Thursdays, 8:30-9 p.m.). Frisky, amiable Sinbad is the victim of what has become a standard sitcom mistake: A show is built around the performance persona that a skilled stand-up comedian has carefully cultivated, but then it leaves him stranded without strong scripts or much of a supporting cast. Sinbad plays a computer-games inventor who takes in two youngsters (Willie Norwood and Erin Davis); that’s it, as far as the premise goes. The comedian spends the half hour smiling warmly, selling flimsy punch lines, and being the object of such lines as, ”You got the highest butt I ever seen on a man”-one of the lowest jokes of the season thus far. C-