"Modern Family" star Eric Stonestreet picked the fight between himself and a Cardinals fan this weekend at the Dodgers game -- this according to the Cardinals fan, who tells TMZ, Stonestreet took a friendly rivalry WAAAY over the line.
The Cardinals fan in question -- a guy named Michael Gallagher -- says the drama began when he heckled Matt Kemp for grounding out at the bottom of the 8th.
Gallagher says he yelled, "Hey Kemp, 0 for 4, nice job!" ... and Kemp rolled his eyes, laughing it off.
According to Gallagher, Stonestreet was sitting next to him and yelled back, "Matt Kemp should've come over and punched you in the face."
Gallagher claims Stonestreet then approached a security guard and said something to the effect of ... "Someone needs to kick this guy's ass."
Gallagher tells us, Stonestreet continued to yell insults at him and his friend, such as "Nice v-neck" -- and finally his friend snapped, yelling back, "Well you're a fat ass!"
According to Gallagher, that's when things got out of hand -- and the actor came over to exchange words up close.
Security quickly intervened and escorted everyone up to the main concourse -- at which point Gallagher says Stonestreet whipped out the infamous line ... "Don't you know who I am?"
Gallagher says security let Stonestreet go back to his seat, but kicked him and his friend out -- for no good reason. As for Stonestreet, the "Modern Family" actor told us nothing happened, despite admitting he was escorted out of his seat.