  With the goal of building a concrete co-dimension one holographically dual
field theory for four dimensional asymptotically flat spacetimes (4d AFS) as a
limit of AdS$_4$/CFT$_3$, we begin an investigation of 3d Chern-Simons matter
(CSM) theories in the Carroll regime. We perform a Carroll (speed of light
$c\to0$) expansion of the relativistic Chern-Simons action coupled to a
massless scalar and obtain Carrollian CSM theories, which we show are invariant
under the infinite dimensional 3d conformal Carroll or 4d Bondi-van der
Burg-Metzner-Sachs (BMS$_4$) symmetries, thus making them putative duals for 4d
AFS. Concentrating on the leading-order electric Carroll CSM theory, we perform
a null reduction of the 3d theory. Null reduction is a procedure to obtain
non-relativistic theories from a higher dimensional relativistic theory.
Curiously, null reduction of a Carrollian theory yields a relativistic
lower-dimensional theory. We work with $SU(N) \times SU(M)$ CS theory coupled
to bi-fundamental matter and show that when $N=M$, we obtain (rather
surprisingly) a 2d Euclidean Yang-Mills theory after null reduction. We also
comment on the reduction when $N \neq M$ and possible connections of the
null-reduced Carroll theory to a candidate 2d Celestial CFT.
