To
steal the show is to unexpectedly become
the
star performer. A performer, be it an
actor,
a
musician, a
comedian, or a
freak show geek,
is said to "steal the show" if their performance is
clearly the best one in the show, especially if it is
better than that of the performers who got
top billing.
For example,
Pinky and the Brain stole the show from the
Animaniacs (so much so that the WB
had to spin off the former). In some concerts,
sideman John Coltrane would steal the show
from bandleader Miles Davis - not an easy task!