  In this article, we present explicit evidence that maximal chaos occurs for a
generic, probe quark-like defect degrees of freedom, in a strongly coupled
large $N_c$ gauge theory. In holography, this corresponds to the dynamics of
open string degrees of freedom, in the background of a closed string geometry.
In this context, we explicitly show that a Schwarzian effective action for the
soft sector emerges and couples with other modes, in the infra-red. This is
manifest on an open string worldsheet, as well as a D$1$-brane world-volume,
embedded in AdS$_3$. The corresponding maximal chaos is governed by an
intrinsic defect D-brane horizon, and an intrinsic non-linear description of
the brane or the string. We also present explicit evidence of maximal chaos
away from extremality on a D-brane horizon, by computing a four-point
out-of-time order correlator of spin-one operators. This further suggests that
a similar description of the soft sector physics of open string degrees of
freedom may exist in general.
