NFL's Montae Nicholson Fight Video Shows Brutal Knockout Punch

2:10 PM PT -- The Redskins announced they placed Montae on the Reserve/NFI list.

10:48 AM PT -- Redskins coach Jay Gruden says Nicholson will NOT play this weekend in their critical game against the Tennessee Titans.

Gruden says he's aware of the TMZ Sports video and says he'll take a look at it.

When asked if Nicholson would be benched for the rest of the season, Gruden said he hasn't made up his mind yet.

He still has to speak with Montae personally.

TMZ Sports has obtained footage of Washington Redskins safety Montae Nicholson pummeling a man in the middle of a Virginia street around 2 AM Tuesday morning ... and it's violent.

Nicholson -- wearing a red hoodie -- is going after another man in a jean jacket while other people in the melee desperately try to restrain him.

But, Nicholson is too strong and too angry -- and refused to back out ... instead, he throws several punches at his target ... including a knockout blow.

You can see in the video, the man in the jean jacket appears to go limp as Nicholson hits him clean in the face.

One witness tells us the other man in the red sweatshirt was trying to break up the fight -- but Montae was in such a rage, he slammed that guy to the ground and continued the beating.

Loudoun County Sheriffs eventually responded to the scene and arrested both Montae and a female companion. Montae was booked for assault and battery, and drunk in public. He was hauled to a nearby jail and released on a $2,500 bond a short time later.

23-year-old Montae -- 6'2", 215 lbs -- is a solid player for the Redskins who's played in every game this season.

There are reports the fight began after a road rage incident where the victims pulled up in a vehicle and honked at Montae.

But, a witness tells us ... the beef started BEFORE the car incident.

Both victims were taken to a nearby hospital where they were treated for serious injuries.

We've reached out to Montae's camp for comment. So far, no word back.

A rep for the Redskins tells us they are aware of the arrest and still gathering information.