Daniele De Santis, a Roma 'ultra' is accused of shooting Ciro Esposito during clashes with Napoli fans who were in Rome for the Coppa Italia final against Fiorentina.
Esposito died from his injuries 53 days later.
Lawyers for De Santis told the final session of his trial that he had acted in self-defence.
Prosecutors are seeking three-year prison terms for two Napoli fans involved in the violence in the Tor di Quinto suburb of Rome.
Verdicts are expected at the end of May.
Ultras are gangs of fans who pride themselves on their dedication to their clubs and are frequently associated with the violence that continues to blight Italian football.
The incidents before the 2014 Cup final made headlines around the world.
At least five police were injured trying to break up a string of clashes between Roma and Napoli ultras in the hours before the match.
After a 45-minute delay to kick-off, a decision was made to go ahead with the game. Napoli beat Fiorentina 3-1 in a final played largely in silence.