Q. Our priest seldom wears clerical attire. He often comes over to the church in athletic clothes. Is this right?
A. Here’s a reply from Msgr. Charles Pope:
A priest should generally wear clerical attire. Canon Law says, “Clerics are to wear suitable ecclesiastical garb according to the norms issued by the conference of bishops and according to legitimate local customs” (Canon No. 284). The U.S. Conference of Catholic Bishops says, “Outside liturgical functions, a black suit and Roman collar are the usual attire for priests. The use of the cassock is at the discretion of the cleric” (Index of Complimentary Norms, No. 3).
Thus, clerical attire ought to be worn. There can be common-sense exceptions perhaps, e.g., when playing sports, at a picnic or on a day off, etc.