Game 4 of the ALCS was filled with memorable moments, from Mookie Betts throwing a laser to gun down Tony Kemp at second base to Andrew Benintendi’s game-ending diving catch (with the bases loaded, no less). However, the one moment that will linger in the minds of baseball fans the longest (especially those who cheer for the Astros) was a controversial fan interference call all the way back in the first inning.

Already down 2-0, the Astros had Jose Altuve at the plate with a man on base. He unloaded an opposite field shot that would have cleared the fence, if not for Mookie Betts making an outstanding leaping stab to attempt to catch the ball.

Except he didn’t catch it.

Either due to an outstretched hand of a fan or simply because it was a really hard catch to make, Betts didn’t come down with the ball in glove. That’s a home run.

Except it wasn’t.

Right field umpire Joe West immediately called Altuve out for fan interference. And there is a case to be made for it, but let’s examine the relevant MLB rule first:

No interference shall be allowed when a fielder reaches over a fence, railing, rope or into a stand to catch a ball. He does so at his own risk. However, should a spectator reach out on the playing field side of such fence, railing or rope, and plainly prevent the fielder from catching the ball, then the batsman should be called out for the spectator’s interference.

It boils down to this: if the ball was already passed the yellow line, and Betts reached into the stands to attempt a catch, then all fan interference is allowed because Betts has technically left the field of play. If the ball hadn’t crossed the yellow line, then the fan is reaching out into the field of play and that makes fan interference a thing that is possible.

So, did Betts reach into the stands? Or did the fan reach into the field?

Here’s the play from a ton of angles:

The play was reviewed, and the official decision was “Call Stands.” It should be noted that there is also a potential decision of “Call Confirmed,” which replay officials did not grant in this case. That means that even if they aren’t sure the call on the field was correct, they can’t find enough evidence to overturn it. Thus, the call made by West stands.

After the game, West spoke to reporters about the call. The exchange was… well, interesting.

Q. What did you see that prompted the initial call of fan interference?
JOE WEST: Well, when he jumped up to reach for the ball, the spectator reached out of the stands and hit him over the playing field and closed his glove.

Q. So the ball had not yet crossed the railing?
JOE WEST: No.

Q. And Betts’ glove had not yet crossed the railing, do you believe?
JOE WEST: No.

Q. Okay. Did the fan —
JOE WEST: Here’s the whole play, here’s the whole play. He hit the ball to right field. He jumped up to try to make a catch. The fan interfered with him over the playing field. That’s why I called spectator interference.

Q. So it’s a clear call in your mind?
JOE WEST: Yes.

Q. Were there already — was there a single call that you saw, that the replay officials saw on replay that confirmed —
JOE WEST: I don’t know what he saw. He just — the replay official said I was right.

Q. Okay.
JOE WEST: That’s all. He said I have nothing that can change it.

Sure, the play happened in the first inning and the Astros had eight more innings to score some runs. And they still allowed the Red Sox to score eight runs of their own, so it’s foolish to say this call absolutely cost Houston the game. But it did cost them two runs, which is the margin they lost by. They are now down 3-1 and facing an elimination game Thursday night.