  Top-quark pair production is central to many facets of LHC physics. At
leading order, the top and anti-top are produced in a back-to-back topology,
however this topology accounts only for a minority of $t \bar t$ events with
TeV-scale momentum transfer. The remaining events instead involve the splitting
of an initial or final-state gluon to $t \bar t$. We provide simple
quantitative arguments that explain why this is the case and examine the
interplay between different topologies and a range of variables that
characterise the event hardness. We then develop a method to classify the
topologies of individual events and use it to illustrate our findings in the
context of simulated events, using both top partons and suitably defined
fiducial tops. For events with large $t \bar t$ invariant mass, we comment on
additional features that have important experimental and theoretical
implications.
