We investigate the fluctuations induced by irrationality in simple gam
es with a large number of competing players. We show that Nash equilib
ria in such games are ''weakly'' stable: irrationality propagates and
amplifies through players' interactions so that huge fluctuations can
result from a small amount of irrationality. In the presence of multip
le Nash equilibria, our statistical approach allows to establish which
is the globally stable equilibrium. However, characteristic times to
reach this state can be very large.