Josh Allen, Hailee Steinfeld Host Epic Halloween Party For Buffalo Bills

Here's further proof Josh Allen and Hailee Steinfeld's relationship is pretty serious ... the two threw on a couples' costume and hosted a huge Halloween bash for all of Allen's Buffalo Bills teammates.

The party went down on Monday night -- and it was officially dubbed "Josh & Hailee's Circus Showdown 2024."

Allen wore a ringleader red coat and black top hot for the occasion, while Steinfeld wore a similar -- yet far sexier! -- get-up.

Almost all of Allen's teammates and their WAGs were in attendance ... and check out some of the images from the festivities, it looked like a blast.

There were balloons, carnival games, a photo booth and some custom drinks -- including a "Freakshow Fizz" tequila cocktail.

There was also a costume contest -- and it appears one of Allen's pals who was dressed as Ben Stiller from "Dodgeball" took home first place.

Allen and the Bills, of course, were not the only team to celebrate Halloween a bit earlier this year ... the Detroit Lions appeared to throw a whale of party for their players Monday night too.

Jared Goff and Amon-Ra St. Brown were there -- as was Goff's wife, Christen, who played the part of Carley Bobby really well.

While trick-or-treating formally begins Thursday ... it's likely these will be the last Halloween parties of the week for NFLers --- Sunday is, after all, just five days away.