According to legal docs, obtained by TMZ, Russell Nielsen got hit with one count of 3rd-degree assault in the County of Maui. Prosecutors say he intentionally, knowingly or recklessly caused bodily injury to Miles.

Now, MT didn't look too roughed up or bothered in the immediate aftermath of the tussle earlier this year -- but it looks like he did bring home a shiner from it, which was clearly visible in photos of him once he touched down in L.A. again. So, yeah ... it would appear prosecutors feel Nielsen left enough of a mark to move forward here.

TMZ broke the story ... Miles says he was confronted by two guys in the bathroom of a restaurant while out dining with his wife, Keleigh, which then allegedly escalated into violence. Miles initially made it out like he'd been cornered and jumped by complete strangers ... as did Keleigh.

Of course, since then ... some of the pieces have fallen into place over what exactly happened and why. We've heard from people familiar with the matter Nielsen knows the Tellers through his own wife, who owns a wedding planning company -- and who apparently worked on Miles and Keleigh's ceremony at one point or another in 2019.

Our sources told us Russ was confronting Miles over money he believed they still owed for wedding planning -- some $60k worth ... and after some talking, allegedly took a swing.

We've gotten video of Russell and his wedding planner wife in other heated situations with folks in the past -- and there, too, he appeared to fly off the handle with his boo egging him on.