A disabled Washington cabdriver saw his $300,000 court award reduced to zero yesterday, when the D.C. Court of Appeals ruled that the Penn Central Railroad was not liable for an assault committed by one of its brakemen.

Cabdriver Arthur Z. Reddick was having a routine day on the job six years ago when he stopped at Union Station to use the men's room.On his way into the building, he was approached by brakeman Frederick Jones, who demanded a ride to Alexandria -- immediately.

When Reddick announced that the trip to the restroom was his first priority, an argument and then a fight ensued, and Jones, wearing steel-toed brakeman's boots, knocked Reddick to the floor and kicked him repeatedly, according to D.C. Superior Court records. Reddick's right leg was shattered in the incident.

Jones eventually pleaded guilty to assault and later a Superior Court jury awarded Reddick $500,000 damages -- to be paid by Penn Central.

Yesterday's appeals court decision threw out the award, which had already been cut to $300,000, because the brakeman was acting "outside the scope of his employment."

Chief Judge Theodore R. Newman Jr., Judge J. Walter Yeagley and Judge John W. Kern III found that Jones' actions were not committed "to further the interest or to serve the purpose" of his employer.

"The mere existence of the master and servant relationship is not enough to impose liability on the master," the judges declared in an 11-page ruling. "The servant is generally not within the scope of his employment when he 'punishes persons who annoy him in the performance of the service.'"

Mrs. Reddick dropped out of college to support the family while her husband underwent rehabilitative therapy, according to Epstein. The couple fell behind on many of their bills, he added, and were counting on the court award to catch up.

The Reddicks were too "upset" to comment yesterday, Epstein said.

"This decision certainly comes as a blow to the Reddicks," said attorney David Epstein, who had argued their case before Superior Court Judge Robert A. Shuker. "Mr. Reddick has been incapacitated for nearly four years. His family has lost the benefit of his income. This decision means that he can never receive any compensation for what has happened."

Epstein, who said he represented the Reddicks on a contingency basis, added that he and his staff have invested about 1,300 man-hours in the case -- time he values at more than $100,000. "We'll just have to absorb the loss this time," he said yesterday.

No new trial can be held on the incident because all the available facts were presented in the first trial, Epstein said. The appeals court finding essentially removes the grounds for the Reddicks' suit, a suit based on Jones' employment with Penn Central, he said.