DENVER (KDVR) — COVID masks trigger more fights on flights than anything else.

A flight was diverted to Denver on Wednesday evening after a passenger allegedly assaulted a flight attendant.

The incident underscores a trend. More flyers are losing their cool than ever before. According to Federal Aviation Administration spokesperson Eva Lee Ngai, the number of unruly passengers went up so dramatically last winter that it started tracking them for the first time. Till then, there were steady from year to year.

“While we did not track unruly-passenger reports prior to 2021, we can say with confidence that based on our experience, the number of reports we’ve received this year is significantly higher than the numbers we’ve seen in the past,” wrote Ngai in an email.

Though the FAA did not track unruly passenger reports before 2021, it did track the number of reports that ended up under investigation.

Records show that number skyrocketed.

From 2006 through 2020, the number of investigated reports hovered around 150 per year. In 2020, there were 183.

In 2021, that spiked to 923 investigated reports.

The rate of unruly passenger reports alone only took a few months to explode.

FAA records say there were 2.45 unruly passenger incidents per every 10,000 flights in the fourth quarter of 2020.

They shot up in the first quarter of 2021. At its highest point, the rate of unruly passengers per 10,000 flights was six times greater than the quarter before with 13.

Most of these unruly passenger reports involve masks.

Of 4,941 reports, 3,580 were mask-related. That’s 72%.