Johnny Manziel: Hawaiian Punch ... QB In Island Altercation

Johnny Manziel was involved in a fistfight at a fancy Hawaiian resort the night before his friend's wedding, TMZ Sports has learned ... but the QB insists he wasn't the aggressor.

Here's what we know ... Manziel was at the Four Seasons Resort on the Big Island on Friday night when he got into it with another wedding guest.

We're told things had been heated between the guys for a while -- but it all came to a head at the rehearsal dinner.

Sources connected to Manziel tell us the QB felt like he was being hounded by the other man. We're told Johnny was adamant he was not the instigator.

But things escalated ... and at one point during the altercation Manziel struck the other guy in the face.

We're told the fight was over almost immediately. We spoke with police who tell us they were NOT called to the hotel that night. We also reached out to Manziel multiple times -- so far, no comment.

But get this ... the next day, the other guy in the fight got a surprise from room service -- a bottle of champagne and a note that read, "Truly apologize. Should have never done that. Know this won't make it better, but hope it starts the day off alright."

It was signed by Johnny Manziel.

One more thing ... Johnny posted a photo from the day of the wedding with a bandage on his finger.