  We study a two-person game played on graphs based on the widely studied
chip-firing game. Players Max and Min alternately place chips on the vertices
of a graph. When a vertex accumulates as many chips as its degree, it fires,
sending one chip to each neighbour; this may in turn cause other vertices to
fire. The game ends when vertices continue firing forever. Min seeks to
minimize the number of chips played during the game, while Max seeks to
maximize it. When both players play optimally, the length of the game is the
{\em toppling number} of a graph $G$, and is denoted by $\tg(G)$.
  By considering strategies for both players and investigating the evolution of
the game with differential equations, we provide asymptotic bounds on the
toppling number of the complete graph. In particular, we prove that for
sufficiently large $n$ $$0.596400 n^2 < \tg(K_n) < 0.637152 n^2.$$ Using a
fractional version of the game, we couple the toppling numbers of complete
graphs and the binomial random graph $G(n,p)$. It is shown that for $pn \ge
n^{2/\sqrt{\log n}}$ asymptotically almost surely
$t(G(n,p))=(1+o(1))p\tg(K_n)$.
