Adrian Peterson Watches ... As Paparazzo EATS CONCRETE!!!

Funny moment with NFL superstar Adrian Peterson ... when our guy was shooting the Minnesota Vikings running back in D.C. yesterday ... and fell ... HARD!!

It's pretty funny ... we were talking to A.P. about gay athletes in professional sports -- and he gave an interesting answer -- but that's when a stationary orange construction cone TOTALLY ATTACKED OUR PHOTOG!!

Our guy never saw it coming and went crashing to the ground as Adrian did the play-by-play -- "Down goes Frazier!!"