This double play ended the game between the Reds and the Brewers, August 26, 2021. With one out in the 9th inning, a soft line drive was hit to Reds shortstop, Jose Barrero. Barrero caught the ball and then lunged forward in an attempt to tag Jace Peterson, the runner at 2B who had moved off the base. As Peterson danced back to the base, he was ruled out of the base path by 2B umpire, Chad Fairchild.
Once a fielder moves toward a runner to make a tag attempt, the runner, he has 6ft (3ft on either side of the imaginary straight line from his place to the base) to avoid the tag. This video explains the rule and shows clearly what the umpire looks for when making this call.
The “out of the baseline” call is umpire interpretation and not subject to replay review.