10:08 AM PT -- A rep for the Irving PD tells TMZ Sports ... Johnny showed NO signs of intoxication.
As for how the whole thing got started, Manziel told police he was being harassed by an 18-year-old man who was hounding him for an autograph.
When the man realized Manziel wasn't going to give him one, Johnny claims the guy started "talking trash" and Johnny responded by throwing the water bottle.
Security stepped in ... and the cops came as well ... but in the end, no one was arrested and everyone went their separate ways.
Johnny Manziel allegedly got into a fight with a buddy of his after a golf tournament Saturday and according to one eyewitness ... Johnny's throwing arm was way off.
Johnny and a group of friends were leaving the Byron Nelson Golf Classic in Irving, Texas, near Dallas, when he got into an argument with a guy in his group. The eyewitness tells TMZ Sports, the guys were yelling at each other when Johnny threw a water bottle "really hard" at the guy, but missed.
The eyewitness tells us, Johnny's friend sarcastically screamed, "Nice throw, Johnny," which apparently enraged the Cleveland Browns QB. The eyewitness says Johnny charged his friend, but was stopped by someone in his group.
Off duty cops who were working security came quickly, spoke with Johnny and his friend, and calmed the situation down. The pic shows Johnny sitting in a chair and talking to a cop by the Four Seasons hotel.
We believe no arrests were made.
Johnny's rep told a reporter the QB was being harassed.