During the singer's "Eras" tour stop in Indianapolis over the weekend, a fan wearing a Travis Kelce costume tried to get the attention of the Kansas City Chiefs tight end ... who popped up in the VIP section of the stadium to cheer on his superstar girlfriend.

As the passionate Swiftie -- who donned a full NFL getup, helmet and all -- tried to get Travis to look over at her, the guard grabbed her by the elbow and began guiding her away from the floor.

Check it out ... you can hear the security detail informing the fan that her helmet was not allowed inside the stadium and telling her she had to "go."

Thankfully, Austin witnessed the whole exchange and swooped in to de-escalate the situation.

He instructed the security guard ... "Hey, let’s not put hands on people."

Austin even went so far as to apologize to the Swiftie and compliment her "really cool costume." He added ... "You guys enjoy the concert. Have a great night."

Austin wasn't the only famous sibling to take action this weekend ... as Jason Kelce sparked controversy after smashing a disrespectful heckler's phone after he called Travis a homophobic slur -- yet chose to repeat the insult himself.

But, the Swifts and the Kelces appeared to shake off the drama, with Taylor showing her boyfriend's family all sorts of love at TK's game Monday evening.

For instance, Taylor, who brought mom Andrea and dad Scott to the game, was caught celebrating one big touchdown alongside Kelce matriarch Donna. She later scooped Jason up into a big hug while taking in the game from a private suite at Arrowhead Stadium.

We're sure her show of support meant a lot to the retired NFL player, as he later issued an apology for his response to the heckler.