Blocking the plate

I think the official rule is that he must have the ball or be in the action of catching the ball, but I don't think I've every seen it inforced.

I've always thought it was unfair, at the non-Professional levels, when a runner can't run over a player blocking a bag, or plate, long before they have the ball. We once ran into a team where the coach taught the first baseman, when holding a runner, to stand between the runner and the bag about two feet off the bag. We couldn't get the umps to call obstruction, his ruling was that they could still go around him.

Obstruction would be the correct call if the situation is a fielder hindering an attempt by a runner to advance or return to a base. Interference involves a runner hindering a fielder from making a play on the ball, but can also include the act of a fielder preventing a batter from offering at a pitch (catcher's interfernce.)

In both the situations described, I believe the correct call would be that there is no obstruction.
For the OP, the catcher is in the act of fielding a thrown ball that is close enough to make a play imminent. From Obrady's post, standing in the runner's path back to the base is not obstruction in and of itself, but may rise to obstruction when the runner attempts to return to the bag.

Agree with Rex that it's not obstruction if the ball is on the way.

I never thought it made any sense for a first baseman to be in the basepath blocking the runners return to the bag - it would be kind of hard to field a thrown ball while laying flat on his back.

Many questions have been posed regararding this situation in the time I've been a member on this site. Almost every time I read one I think: "Had to be there".

The OP says that the runner arrived about a second before the ball did. Well, in terms of the distance a thrown ball can travel in a second, the ball could still be quite far away when the runner arrived and slid into the catcher.

For a catcher to block legally he must be in possession of the ball or the play must be immenent. Immenent means different things to different people.
To me, immenent means the thrown ball needs to be close to being received by the catcher as he drops to block the plate. But that's just me. Another umpire may see it differently.

Without seeing the play in question it's just too difficult to give an accurate answer.

As a coach , based on what is described, I would expect a "bang bang" play and a collision ( I caught)---and it would all be sorted out after the play

When NFHS (eventually) changes to match the NCAA rule, life will be a lot easier for all of us.

I call it like Pilsner, maybe a little looser. I like the way OBR is called in that if the ball takes you there it's OK. If you go there and make the throw come to you then it's obstruction. This isn't exactly the way it's worded but that's the way I've always called it.
Many feel if the ball is in the air at all then it gives the fielder the right to be there. This simply isn't true and is the reason NCAA and LL changed their rules to make the obstruction harder to ignore. Many umps were catchers and they err on the side of letting catchers do what they want. This really isn't the correct way to call it.