Pittsburgh Steelers -- BIZARRE PREGAME RITUAL ... Face Down, Legs Up

Well, this is weird.

The entire gang of Pittsburgh Steelers linebackers performed their pre-game ritual with LB coach Joey Porter before Sunday's game against the Browns ... and it was all caught on video.

Here's how it went down ... the LB crew lines up to give Porter a high-five ... each player getting lower to the ground than the guy before him -- culminating with a bizarre tandem leg-raising finale.

It's weird ... but if it works, who are we to judge ... right?