There is no simple answer to whether applause is appropriate in the liturgy. It really depends on who the Catholics are and why they might be clapping!
Applause is never called for per se in the rubrics that govern our rites. But sometimes the liturgy gives an instruction like this, from the rite to send those preparing for Baptism to the cathedral for the Rite of Election on the First Sunday of Lent: “When appropriate in the circumstances, the celebrant may also ask the whole assembly to express its approval of the candidates [for the sacraments of initiation].”
A natural way to express such approval may be for all to clap, making this kind of applause appropriate. Such applause is a form of acclamation, and the liturgy often calls for acclamation.
At a parish in the Archdiocese of Chicago, where the scriptures are deeply revered and the Easter Vigil is celebrated with great care, spontaneous applause broke out one year at the end of the gospel procession, after the Book of the Gospels was carried around the room to the joyous singing of the Alleluia. It has since become an annual custom.
It’s appropriate because it is an acclamation by the assembly of Christ s presence in the gospel, as well as an expression of sincere gratitude for the return of the Alleluia, from which we fast during Lent.
In some African American Catholic communities, it’s customary to clap sporadically during the homily, both as a way of acclaiming or affirming something just said and as a general sign of support and encouragement for the priest or deacon preaching. This is appropriate if it’s spontaneous (never invited by the preacher!) and if it encourages everyone’s participation in the homily through active listening.
In some cultures an important part of singing is clapping as a kind of accompaniment. This, too, could be an appropriate way of promoting that full, conscious, and active participation in the liturgy to which all baptized people are called.
Perhaps the kind of clapping least appropriate to the liturgy is the applause that an audience offers to performers or to athletes. In the liturgy all baptized people are the “performers”; we are all spiritual “athletes.”
It’s important to show our gratitude for those among us who volunteer their time and talent–especially the choir. But instead of polite applause, we’d do better to create a climate of gratitude with occasional bulletin kudos, surprise refreshments at rehearsals now and then, an annual appreciation dinner, and the like.
But spontaneous applause that breaks out after liturgy need not worry us. It doesn’t offend–and it may even delight–God. And it usually dies down soon enough for those who need some quiet time.