  We discuss magnetotransport in a low density electron gas coupled to spin
fluctuations near and above a ferromagnetic transition. Provided the density is
low enough ($n \lesssim 1/\xi^{3}(T)$, with $\xi(T)$ the ferromagnetic
correlation length), spin polarons form in an intermediate temperature regime
above $T_c$. Both in the spin polaron regime, and in the itinerant regime
nearer $T_c$, the magnetoresistance is large. We propose that this provides a
good model for ``colossal'' magnetoresistance in the pyrochlore
Tl$_{2-x}$Sc$_x$Mn$_2$O$_7$, fundamentally different from the mechanism in the
perovskite manganites such as La$_{1-x}$Sr$_x$MnO$_3$.
