1
general::
Goad or urge ahead, as in The thought of winning a Pulitzer Prize spurred the reporter on. This expression transfers using spurs to make a horse go faster to incentives of other kinds. [Late 1500s]
American Heritage Idioms
2
general::
Phrase(s): spur someone on
to urge someone onward; to egg someone on. (Fig. on applying spurs to a horse.) • The crowd spurred the runners on throughout the race. • The cheering spurred on the runners.
McGrawhill's American Idioms And Phrasal Verbs