Like a column starting a row, perhaps

LIBELLOUS

Think of a defamatory word where the first letter might lead a spreadsheet’s first cell.

This clue plays on the word "column" in two ways. In printing, a "column" can refer to a vertical block of text, and "libellous" (meaning defamatory) might describe something written in one—like a newspaper article starting a row (or controversy). The "starting a row" part hints at the wordplay, where "libel" (a written defamation) is stretched into "libellous" to fit the grid.