Beginning 2024, pro rules (OBR, MLB) will no longer allow a fielder who is not in possession of the ball to block a base (1B, 2B, 3B) or impede a runner. It will be enforced similar to the Home Plate Collision Rule. 

New Rule Explained Here:

https://baseballrulesacademy.com/obstruction-enforcement-at-all-bases-in-2024/

In the July 24 Blue Jays-Mariners game in Seattle, Jays catcher Dioner Navarro picked off Brad Miller at third base. There was some question whether or not Jays third baseman Josh Donaldson obstructed the runner’s path to the base.

If you view the play, you will notice that Donaldson blocked the base with his knee as he received the throw from Navarro. Miller had no where to go and was called out after making minor contact with Donaldson.

Did Donaldson obstruct Miller?

My answer is “No.”

I think the key here is that Donaldson caught the ball as he simultaneously lowered his right knee to block the base. James Loney does this at first base on pick off throws. If Miller had barreled over Donaldson, it would have been a legal move on Miller’s part-the same holds true for plays at the plate when a runner collides with a catcher who has possession of the ball while blocking the plate. But you seldom see a runner barrel over a fielder on a pick-off attempt. If this happened more to fielders, they probably wouldn’t block the base so aggressively.

But by rule, Donaldson did not obstruct Miller because he had the ball when he blocked the base. If he had blocked the base before Navarro threw the ball, or was not in the act of fielding the throw, Donaldson should have been called for Type A obstruction because a play was being directly made on Miller at the time of obstruction. The ball would be dead and Miller would score. In Type A obstruction plays, the runner is awarded one base from his last legally touched base. In the above play, Miller’s last legally touched base was third base so he would be awarded home even though he was returning to third base.

The most common Type A obstruction plays occur when a runner is obstructed by a fielder without the ball in a rundown or when a batter-runner is obstructed by a pitcher covering first base without the ball in his possession while the ball is in the infield.