Dynamic recrystallization (DRX) is almost universally observed in the microstructure of adiabatic shear bands. It is usually admitted that DRX results from the large temperatures that develop in the band along with very high local strains. This paper reports the observation of dynamically recrystallized nanograins in Ti6Al4V alloy specimens that were impact loaded to only half the failure strain at which the adiabatic shear band develops. This observation shows that DRX not only precedes adiabatic shear failure but it is also likely to be a dominant micromechanical factor in the very generation of the band. This result means that adiabatic shear failure is not only a mechanical instability but also the outcome of strong microstructural evolutions leading to localized material softening prior to any thermal softening.