On A Roll Meaning

(idiomatic) Having a streak of good luck or good progress or success.

Example:   He was on a roll with the answers that day and didn't want to stop.
1984 Jan. 2, Charles P. Alexander, "Cheers for a Banner Year," Time (retrieved 26 Aug 2015):
  With unemployment falling, incomes rising, inflation at bay and shoppers crowding into stores, the economy is entering 1984 on a roll.
2015 Feb. 9, Matthew Amalfitano, "Torino eyeing Europa League," Independent (UK) (retrieved 26 Aug 2015):
  After a sluggish start to the season, Torino are on a roll. The Granata began their nine-match unbeaten streak in Serie A on December 6.