My son was in a fight and arrested pending the investigation. Can a public defender do the job in representing him? Or do I need a specialist? (I wonder if the public defenders are overworked and underpaid).

Public defenders are specialists. They represent people charged with crime every day. They are experienced at evaluating cases, investigating them and negotiating plea bargains. If your son wants to take the case to trial, they are skilled trial attorneys. Public defenders can be overworked and they are definitely underpaid. They know this will be the case before they accept the job. They become accustomed to their caseload and efficient at handling it. They also receive assistance when needed from other lawyers and support personnel in their office. Public defenders are not only qualified and experienced attorneys, they are among the profession's most dedicated lawyers. We are lucky to live in a country that provides such skilled counsel at no charge to those who can't afford counsel. If your son qualifies financially for a public defender, I would go that route. If a problem develops in their relationship later on, you can always seek out private counsel at that point.