A 21-year-old man from Birżebbuġa was injured in an argument during the morning band march of the feast in his hometown on Sunday.
His condition is not yet known.
The police said the incident happened in Triq Birżebbuġa at around 2.15pm.
A knife was used and a 68-year-old man, also from Birżebbuġa, has been arrested.
The band march was cut short as a result.