We investigate the crossing-symmetry relation between b →c τ-ν ¯ decay and b c ¯→τ-ν ¯ scattering to derive direct correlations of new physics in semitauonic B -meson decays and the mono-tau signature at the LHC (p p →τhX +MET ). Using an exhaustive set of effective operators and heavy mediators we find that the current ATLAS and CMS data constrain scenarios addressing anomalies in B decays. Pure tensor solutions, completed by leptoquark, and right-handed solutions, completed by WR' or leptoquark, are challenged by our analysis. Furthermore, the sensitivity that will be achieved in the high-luminosity phase of the LHC will probe all the possible scenarios that explain the anomalies. Finally, we note that the LHC is also competitive in the b →u transitions and bounds in some cases are currently better than those from B decays.