  The so-called sdA stars are defined by having H-rich spectra and surface
gravities similar to hot subdwarf stars, but effective temperature below the
zero-age horizontal branch. Their evolutionary history is an enigma: their
surface gravity is too high for main sequence stars, but too low for single
evolution white dwarfs. They are most likely byproducts of binary evolution,
including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and
their precursors (pre-ELMs). A small number of ELMs with similar properties to
sdAs is known. Other possibilities include metal-poor A/F dwarfs, second
generation stars, or even stars accreted from dwarf galaxies. In this work, we
analyse colours, proper motions and spacial velocities of a sample of sdAs from
the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We
define a probability of belonging to the main sequence and a probability of
being a (pre-)ELM based on these properties. We find that 7 per cent of the
sdAs are more likely to be (pre-)ELMs than main sequence stars. However, the
spacial velocity distribution suggests that over 35 per cent of them cannot be
explained as single metal-poor A/F stars.
