NEW YORK (AP) — Airline passengers have come to expect a tiny escape from the confined space of today’s packed planes: the ability to recline their seat a few inches. When one passenger was denied that bit of personal space Sunday, it led to a heated argument and the unscheduled landing of their plane, just halfway to its destination.

The fight started on a United Airlines flight because one passenger was using the Knee Defender, a $21.95 gadget that attaches to a passenger’s tray table and prevents the person in front of them from reclining.