LaVar Arrington -- STOP TRASHING BEYONCE'S HAIR ... 'It's Alright With Me, Bro'

It's been a rough week for Beyonce's hair -- it's been under fire for days after the singer debuted her new short bangs .... but now, an NFL hair expert is finally stepping up to DEFEND B's new do.

The man who's got Bey's back is former Washington Redskins linebacker LaVar Arrington -- who tells TMZ Sports everyone needs to take a deep breath and CALM DOWN about the haircut.

"If she feels good about it, I feel good about it."

Hey, if it's good enough for Lloyd Christmas ...