Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon XXIV

Canon XXIV.

No one who is on the priestly catalogue nor any monk is allowed to take part in horse-races or to assist at theatrical representations. But if any clergyman be called to a marriage, as soon as the games begin let him rise up and go out, for so it is ordered by the doctrine of our fathers. And if any one shall be convicted of such an offence let him cease therefrom or be deposed.

Notes.

Ancient Epitome of Canon XXIV.

A clergyman or monk shall be deposed who goes to horse-races, or does not leave nuptials before the players are brought in.

Van Espen.

Scarcely ever were these plays exhibited without the introduction of something contrary to honesty and chastity.  As Lupus p. 377 here notes, the word “obscene” has its derivation from these “scenic” representations.

Rightly therefore has it been forbidden by the sacred canons that the clergy should witness any such plays.

In the second part of this canon by the words “ordered by the doctrine of our fathers,” the Synod understands the doctrine of the fathers of the synod of Laodicea, which in its canon liv. condemned the same abuse.

Compare the canon given in the Corpus Juris Canonici, Gratian’s Decretum, Pars I., Dist. XXXIV. can. xix.