Comments on the twisted punctures of A even class S theory

We point out that the USp symmetry associated to a full twisted puncture of a class S theory of type A _even has the global anomaly associated to π ₄(USp) = &Z;₂. We discuss manifestations of this fact in the context of the superconformal field theory R _{2,2 N} introduced by Chacaltana, Distler and Trimm. For example, we find that this theory can be thought of as a natural ultraviolet completion of an infrared-free SO(2 N + 1) gauge theory with 2 N flavors, whose USp(4 N) symmetry clearly has the global anomaly.