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Robert Griffin III was physically restrained during a heated confrontation at an off-season training session in Tallahassee ... and TMZ Sports has the video.

Witnesses tell us RG3 was sprinting Monday night at the track stadium at Florida State University (his girlfriend, Grete Sadeiko, is on the Track & Field team) when he accidentally bumped into another runner.

We're told it appeared to be an honest mistake -- but the other man didn't let it go and stepped to the 6'2", 220 pound QB.

You can see in the video Griffin is pissed -- and his GF ultimately grabs him and pulls him away.

We spoke with Sadeiko who told us, "The [other guy] got heated and got way too close to [Robert] but Robert didn’t touch the guy not once nor put his hands on him."

She added, "The guy tried to approach him again while Robert was walking away. I went between so the guy wouldn’t do anything stupid and that was the end of it."