Watch: Altuve loses HR on controversial fan-interference call

Instant replay reared its head again early in Game 4 of the American League Championship Series on Wednesday - this time in a potentially series-changing moment.

In the bottom of the first inning, Houston Astros second baseman Jose Altuve launched a fly ball to right field that narrowly evaded Boston Red Sox right fielder Mookie Betts' glove as he leaped above the fence. Betts couldn't squeeze the ball, which bounced off his glove, then off a fan in the first row, and back onto the field.

But instead of ruling the play a home run, right-field umpire Joe West immediately called Altuve out due to fan interference, and the controversial decision was upheld after a lengthy video review.

MLB's official explanation is that replay officials were unable to find conclusive evidence to overturn the call on the field - specifically, they couldn't determine if the spectator reached over the fence into the field of play - and therefore stayed with the original decision, as relayed by Joe Sherman of the New York Post.

The fan who interfered with Betts on the play was reportedly given a warning and not ejected from Minute Maid Park, according to MassLive's Chris Cotillo.

Because Altuve was called out, the Red Sox maintained their 2-0 lead over Houston.