  The splashback radius $r_\mathrm{sp}$ has been identified in cosmological
$N$-body simulations as an important scale associated with gravitational
collapse and the phase-space distribution of recently accreted material. We
employ a semi-analytical approach to study the spherical collapse of dark
matter haloes in symmetron gravity and provide insights into how the
phenomenology of splashback is affected. The symmetron is a scalar-tensor
theory of gravity which exhibits a screening mechanism whereby higher-density
regions are screened from the effects of a fifth force. In this model, we find
that, as over-densities grow over cosmic time, the inner region becomes heavily
screened. In particular, we identify a sector of the parameter space for which
material currently sitting at $r_\mathrm{sp}$ has followed, during the
collapse, the formation of this screened region. As a result, we find that for
this part of the parameter space the splashback radius is maximally affected by
the symmetron force and we predict changes in $r_\mathrm{sp}$ up to around
$10\%$ compared to its General Relativity value. Because this margin is within
the precision of present splashback experiments, we expect this feature to soon
provide constraints for symmetron gravity on previously unexplored scales.
