I was watching a game the other night and the batter hit a dribbler down 1st base line. The ball started out foul and the umpire immediately called it foul. However, before the catcher could get to the ball, it rolled over the chalk line a few inches into fair territory and stopped. I know it is not a foul ball, but it's really frustrating to see umpires make this call.
Why can't a poster simply make an observation as opposed to asking a question?
Because the thread theme request questions.
To your complaint, it does sound like a premature call unless there were circumstances not included in your post. And some probably don't think it is that big a deal, but as pointed out here, it is. Sometime routine calls become so routine they are assumed and made too early. Part of that is the apathy of those working the game.
About a decade or so ago during an on-field drill in a school, part of instruction to get this point across (to not assume), I stated to the class that "a batted ball is not a foul ball until it actually becomes a foul ball". One of the students was a baseball guy who wanted to get into HS softball (for the $$). Of course, he knew everything because he had attended Harry Wendelstedt's school. He laughed and noted to the other students how "stupid" that comment was and it must have been a softball thing. He really didn't respect the game and was only in it for the money. He never could adjust to the game and my "stupid" comment came back to haunt him later that season when, like in the OP, he called a rolling ball foul that rolled back and hit the side of 3B.
It is just a bad move for an umpire to be quick on a call.