I was afraid you would say that! But thank you for your input.
My subreport for the initial value is shown in the header and then every detail line is shown with the running total as it happens. So the running total may go negative during one of the detail lines and then my flag is set accordingly (using WhilePrintingRecords).
I would like to see all of the detail lines for any group when the flag is set, but I guess I could, at a pinch, sacrifice the detail lines before it is set. The difficulty I foresee is Crystal needs to evaluate and print the entire line before it can decide to suppress it or not and by then it's too late!
I wonder if there are any alternative approaches thinking outside the box, however I also recognise that it is difficult to get your head round someone else's problem based on a short description. If anyone has ideas and would like to probe the problem then please ask for more details.