Answer:

sleeper

AnswerCrossword Clue
SLEEPERUnexpected hit
SLEEPER... of 1973
SLEEPEROne out?
SLEEPERSurprise success
SLEEPERPerson in 39-Down
SLEEPERCertain train car
SLEEPERTrain car / Strips again
SLEEPERTrain car