EXCLUSIVE

We now know why Ezekiel Elliott was in the middle of a police incident at an Ohio bar over the weekend ... his "best friend" was getting arrested for a bringing a loaded gun to the place.

TMZ Sports posted video of Ezekiel speaking with cops in front of the Park Street Patio Bar on Friday night ... and while he was NOT detained, arrested or accused of any wrongdoing -- it's clear he was very interested in the investigation.

Play video content TMZSports.com

Now, we know the person who was arrested that night is Alvarez Jackson ... who's been described as Zeke's "best friend" in a 2015 Sports Illustrated article. He's also a regular on EE's Instagram feed.

According to the police report obtained by TMZ Sports, Jackson was being patted down by security on his way into the bar when they found a loaded Glock 9mm handgun inside of a purse-like bag around his neck.

Security took the gun -- but Alvarez allegedly ran upstairs into the bar. Officials say he was tracked down and arrested.

Law enforcement sources tell us Alvarez tried to name-drop Ezekiel during the incident -- claiming he's the NFL star's "brother."

We previously spoke with Ezekiel's rep who says the Cowboys RB did provide information to police but was NEVER accused of any wrongdoing.