  PSR\,J1723$-$2837 is a "redback" millisecond pulsar (MSP) with a low-mass
companion in a 14.8\,h orbit. The system's properties closely resemble those of
"transitional" MSPs that alternate between spin-down and accretion-powered
states. In this paper we report on long-term photometry of the 15.5\,mag
companion to the pulsar. We use our data to illustrate that the star
experiences sporadic activity, which we attribute to starspots. We also find
that the companion is not tidally locked and infer $P_{\rm s}/P_{\rm b}=
0.9974(7)$ for the ratio between the rotational and orbital periods. Finally,
we place constraints on various parameters, including the irradiation
efficiency and pulsar mass. We discuss similarities with other redback MSPs and
conclude that starspots may provide the most likely explanation for the often
seen irregular and asymmetric optical lightcurves.
