The conductor was attacked by around a dozen people armed with clubs as the regional train was travelling north from Naples to Caserta, Italian media reported.
As the violence unfolded, the train was forced to stop at Casoria, just 14km outside the city, and the vandals dispersed.
The train service was cancelled and around 200 passengers were transferred to buses.
It is the latest in a number of incidents that have occurred on train lines in and around Naples, including the popular Circumvesuviana line which carries around 45,000 tourists and local commuters between Naples and Sorrento every day.
According to Corriere del Mezzogiorno, the number of train travellers has fallen by 196,000 (or 42 percent) in the region of Campania surrounding Naples in the past three years due to delays and inefficiencies.
Legambiente, Italy's largest environment protection group, says Naples needs to replace many old, slow trains to prevent commuters from turning to their cars and raising air pollution levels.
In a recent report entitled “New trains for a more livable city”, the organization said the Campania region needed 117 new regional trains, 40 new trains for the Naples' underground service and 10 new trams.