Completeness-corrected fractions of star forming galaxies as a function of cluster-centric distance. The black solid line shows A 520. The thick dashed magenta line shows the mean of the ten clusters from the comparison sample. The region shaded in magenta shows the spread (±1σ) among the individual clusters. The outermost point, indicated with a large circle, shows f_SF in the near field region. The last radial bin is double the size of the inner ones due to a low number of points. The numbers in each radial bin show the number of galaxies in that bin before correction for completeness (number of star forming galaxies N_SF/total number of galaxies N_all). The magenta and black numbers show the comparison sample and A 520, respectively. The thin lines of different colour show the expected f_SF-radius relation from observations of 75 massive clusters in the Millennium simulation. The star formation in the infalling galaxies is quenched upon passing through R₂₀₀ of the cluster for the first time, with a delay indicated by the different colour, according to the colour bar on top of the plot. f_SF in the infall region of the simulated clusters is normalised to the median f_SF in the near field of the ten comparison clusters.