I go, from time to time, to Mass at other parishes in town. At one particular parish, the pastor, when he is celebrating Mass has taken to introducing a Hail Mary within the Mass. I go to this particular parish’s Masses because they are always reverent and follow the rubrics of the liturgy – perhaps with this one exception. Is this priest out of line with the insertion of a Hail Mary in the body of the Mass?
While no doubt a well-meant gesture, the Hail Mary is not a prayer proper to the Mass and so should not be included in the public prayers of the Mass. How serious a deviation this is would depend on where in the Mass the priest is praying the Hail Mary. If it is during the consecration, it would be gravely problematic. If it is during the general intercessions or during the Communion meditation, it would not be as serious.