Theoretical descriptions and experimental tests of anomalies are crucial for the development of consistent quantum field theory, wherein anomalies emerge as essential features. The process $\gamma \pi\to \pi\pi$, driven by its abnormal intrinsic parity, appears in the anomalous sector of low-energy quantum chromodynamics (QCD). We briefly review the recent theoretical developments underlying this chiral anomaly, focusing on its extraction based on dispersion relations, lattice QCD, and from the crossed channel $\gamma^* \to 3\pi$.