Fail to hold, in a way

SAG

Think of what happens to a hammock when it can't support weight over time, or how a shelf might look if it bends under too many books.

"Fail to hold" hints at something giving way or drooping under weight or pressure. The phrase "in a way" signals we’re looking for a word that means to sink or bend downward—that’s "sag." Think of a shelf that can’t support its load or fabric stretching over time; both "fail to hold" by sagging. The clue plays on the literal weakness implied in the answer.