To grab someone by the front of their shirt and push them backwards.
This can make people think of anger or aggression.
Examples:
He tried to shirtfront the bully.
Don't shirtfront anyone, it's not nice.
She shirtfronted the bad guy and saved the day.
I almost got shirtfronted by my little brother!
The superhero shirtfronted the villain and saved the city.
He shirtfronted the bad guy and made him run away.