  The LAO/STO interface hosts a two-dimensional electron system that is
unusually sensitive to the application of an in-plane magnetic field.
Low-temperature experiments have revealed a giant negative magnetoresistance
(dropping by 70\%), attributed to a magnetic-field induced transition between
interacting phases of conduction electrons with Kondo-screened magnetic
impurities. Here we report on experiments over a broad temperature range,
showing the persistence of the magnetoresistance up to the 20~K range ---
indicative of a single-particle mechanism. Motivated by a striking
correspondence between the temperature and carrier density dependence of our
magnetoresistance measurements we propose an alternative explanation. Working
in the framework of semiclassical Boltzmann transport theory we demonstrate
that the combination of spin-orbit coupling and scattering from finite-range
impurities can explain the observed magnitude of the negative
magnetoresistance, as well as the temperature and electron density dependence.
