  We have performed low-resolution ground-based spectroscopy of HATS-46 b in
transmission, using the EFOSC2 instrument on the ESO New Technology Telescope
(NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for
transmission spectroscopy, having a Jupiter-like radius (0.95 R$_\textrm{Jup}$)
but a much lower mass (0.16 M$_\textrm{Jup}$). It orbits a G-type star with a
4.7 d period, giving an equilibrium temperature of 1100 K. We observed one
transit of HATS-46 b with the NTT, with the time-series spectra covering a
wavelength range of 3900 - 9000 Angstrom at a resolution of $R \sim 380$. We
achieved a remarkably precise transmission spectrum of 1.03 $\times$ photon
noise, with a median uncertainty of $357$ ppm for $\sim 200$ Angstrom wide
bins, despite the relative faintness of the host star with $V_{\mathrm{mag}} =
13.6$. The transmission spectrum does not show strong absorption features and
retrievals favour a cloudy model, ruling out a clear atmosphere with
$3.0\sigma$ confidence. We also place a conservative upper limit on the sodium
abundance under the alternative scenario of a clear atmosphere. This is the
eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as
the NTT to obtain low-resolution transmission spectra of hot Jupiters with
precisions of around one atmospheric scale height.
