  Given a Henselian and Japanese discrete valuation ring $A$ and a flat and
projective $A$-scheme $X$, we follow the approach of Biswas-dos Santos to
introduce a full subcategory of coherent modules on $X$ which is then shown to
be Tannakian. We then prove that, under normality of the generic fibre, the
associated affine and flat group is pro-finite in a strong sense (so that its
ring of functions is a Mittag-Leffler $A$-module) and that it classifies finite
torsors $Q\to X$. This establishes an analogy to Nori's theory of the
essentially finite fundamental group. In addition, we compare our theory with
the ones recently developed by Mehta-Subramanian and Antei-Emsalem-Gasbarri.
Using the comparison with the former, we show that any quasi-finite torsor
$Q\to X$ has a reduction of structure group to a finite one.
