A Quincy man claimed self-defense Tuesday in the stabbing Monday of a motorist who was angry at him for blocking traffic during an episode of road rage that virtually froze traffic on Morrissey Boulevard for hours at the height of the evening commute. Colum Flaherty, 62, said through his lawyer that he was trying to fend off a physical assault by a man who complained that Flaherty was blocking traffic after he was involved in a car accident. The man then started screaming and punching at Flaherty, he said. 'He was scared to death,' said Flaherty's court-appointed lawyer, Jose Vincenty. 'He seemed like a decent man who was involved in a minor accident and road rage got in the way.' Flaherty, a burly man who is on disability after undergoing heart surgery recently, his lawyer said, pleaded not guilty at his arraignment in Dorchester District Court to assault and battery with a dangerous weapon. With his wife of 26 years in court with him, he was released on $500 cash bail. The case was continued to Jan. 5. The other driver and the alleged stabbing victim, Michael McDevitt, 54, also of Quincy, was issued a summons to appear in court at a later date on charges of assault, assault and battery on a person over 60, negligent operation of a motor vehicle, and disorderly conduct. He could not be reached for comment through calls made to his home Tuesday. McDevitt was treated for a stab wound on his right forearm at Massachusetts General Hospital and was released. The incident occurred just after 3 p.m. Monday, when traffic starts to pick up at the Morrissey Boulevard intersection at Freeport Street, near an onramp to Interstate 93. Flaherty's car had just had a minor collision with another car at the intersection, and both motorists parked there so they could exchange insurance information, according to court records. At that point, McDevitt pulled his vehicle up in front of both cars, swearing at Flaherty along the way, the records said, and then stopped and got out. McDevitt and Flaherty give differing accounts about the altercation. But in speaking with a witness, the other motorist involved in the car accident with Flaherty, State Police decided to charge both men. According to court records, McDevitt, angry at Flaherty for blocking traffic at a key intersection, approached the man's car and started pounding on the window. 'Get the ((expletive)) out of my way; I have to pick up my kid,' McDevitt was saying, according to court records. McDevitt said Flaherty swung the door open. Flaherty said McDevitt opened it himself. After that, according to court records citing the third motorist, McDevitt started punching Flaherty. 'Flaherty stated that McDevitt attempted to pull him from the ((the car)),' State Police said in court records. Flaherty told police, according to court records, that he then grabbed a pocket knife he had in his car, with a 3?-inch blade, and stabbed at McDevitt. The wound spilled a large amount of blood in the car and on the roadway, a prosecutor said in court Tuesday. Police established a crime scene that exacerbated the traffic flow. McDevitt was brought to the hospital. Flaherty was arrested. His lawyer, Vincenty, said Tuesday that he will challenge the charges on the grounds that Flaherty acted in self-defense. 'The facts are what they are: He was attacked,' Vincenty said outside the courtroom Tuesday. 'He was scared, scared he would be killed, and he just defended himself. Bottom line.' 