Mr Belichick was filmed dragging his suitcase along towards the changing rooms at Bank of America Stadium in Charlotte, North Carolina.
The clip was later shared by the NFL Network on Twitter.
The coach was wearing a short-sleeved sweatshirt with matching navy sweatpants rolled up, showing his sneakers and long socks.
Twitter users were quick to share jokes about the look.
Dan Crohn wrote that Mr Belichick was “adjusting to daylight savings time”.
“Bill Belichick is all of us walking through the airport hungover at 6am,” Emerson Lotzia, Jr tweeted.
“This is me the morning after I have few too many beers,” another Twitter user wrote.
“If the opposing coach shows up like this, your ass is dead in the water. [I don’t even know] who they play. Don’t matter. Them boys getting clapped,” another account holder wrote.
Adam Heisler wrote that Mr Belichick “stole my weekend attire”.
“It looks like he’s wearing his pants up to his ribs,” Alex Barth tweeted.
Joe Haggerty wrote that Mr Belichick had “some serious ‘Dad that just woke up from a nap’ energy right now”.
“Well, Bill Belichick is a very unique coach, but here he proves he’s just like everyone else, puts his sweats on one pant leg at a time,” one broadcaster said on Sunday.
In September 2020, Mr Belichick appeared at a press conference in a t-shirt covered in holes.
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