From the rulebook:
You score points at the start of each of your turns if one of your runners holds the ball while standing on a scoring mound.
At the end of each period, all teams score points if their runners are standing on scoring mounds, with or without the ball .
Scoring on a minor scoring mound (a “minor score”) is worth 1 point during the 1st period, 2 points dur- ing the 2nd, 3 during the 3rd, 4 during the 4th.
Scoring on your team’s major scoring mound (a “major score”) is always worth 5 points . The other teams’ major scoring mounds aren’t worth anything to you, but it can be worth the effort to prevent them getting there.
So, there are times you only score if you are holding the ball...