In the bottom of the first inning, Jose Altuve hit a fly ball towards the right center fence for a possible two-run home run to tie the game with Boston.
Red Sox outfielder Mookie Betts leaped toward the wall with his glove extended toward fans awaiting a possible souvenir.
The ball went out of play, but right field umpire Joe West called fan interference which effectively meant Altuve was out. Under fan interference rules, an out is called if a fielder's catch that would have been an out was affected by a fan in the stands.
Here is the full definition of Spectator Interference, according to the MLB.
In every case of spectator interference with a batted or thrown ball, the ball shall be declared dead and the baserunners can be placed where the umpire determines they would have been without the interference. When a spectator clearly prevents a fielder from catching a fly ball by reaching onto the field of play, the batter shall be ruled out. But no interference is called if a spectator comes in contact with a batted or thrown ball without reaching onto the field of play -- even if a fielder might have caught the ball had the spectator not been there.
WATCH: Was this fan interference? You decide
An automatic replay review did not have enough evidence to overturn the initial call, making the out stand.
Eyewitness News reporter Nick Natario spoke with fan Troy Caldwell, who is at the center of the controversial call. He was ruled to have interfered with the play.
"Troy, how are you feeling right now? Did you touch the glove?" Nick asked as Caldwell returned to his seat after the incident.
HOME RUN CONTROVERSY: Was it a home run or fan interference? I just went and asked the #Astros fan himself. Troy said without a doubt it should’ve been a home run. #NeverSettle https://t.co/KguuJO5AFf pic.twitter.com/CvVMOKnKLX— Nick Natario (@NickABC13) October 18, 2018
According to Caldwell, the hit was "without a doubt" a home run.
Caldwell later answered Nick's question when he told ESPN that he never touched Betts' glove and it was another fan named Jared who did.
"I never touched his glove, I can guarantee you that. But I definitely touched the ball," Caldwell claims.
After a back-and-forth game, the Astros wound up losing Game 4 by two runs. Natario caught up with the fan as he exited Minute Maid Park to get his thoughts:
"If Boston wins this series, then Joe West is the MVP. I'll give that to you right now," Caldwell added when talking to ESPN.
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Caldwell's brother-in-law said he's fearful Caldwell is going to get death threats over the incident.
Scott Crawford talked exclusively to ABC13 Thursday morning about what his family member has been going through.
"Troy is getting the bad end of the stick. People are going after his family and his job, unjustly as far as I'm concerned," Crawford said.
"That's not fan interference, that's a bad call. Joe West is famous for those. That's not good," he added.
SEE MORE: Jose Altuve says he doesn't blame fan for controversial call
Crawford said he was at his son's football practice when the play, that's been the talk of the sports world for the last several hours, occurred.
He recalls hearing cheering and then, "a few minutes later my wife sends me a picture and says that looks like Troy. 'I said are you sure, it does look like him.' I thought it was a joke. I get home and it is Troy."
Crawford believes the call is getting blown out of proportion, considering the runners the Astros left on base.
"We left bases loaded at end of the game," Crawford argued. "You can't say won or loss by one fan's interference. How can you say it was his fault? Even if it was, even if he interfered, how can you say he cost the game?"
Crawford said his concern is growing over his brother-in-law's safety because some users on Facebook have posted pictures of him along with information about him, pointing out who he is.
He even said that Caldwell bought a blue shirt and crazy hat to minimize being identified.
Caldwell now lives in Atlanta, but because he's a lifelong fan, has returned to Houston often for the games.
His wife told ABC13 he has returned home.
The World Series defending champion Astros face elimination Thursday night, now that they trail the Red Sox in the series 3-1.
Justin Verlander will get the start. First pitch for game 5 is at 7 p.m.
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SEE MORE: ALCS Game 4 live scoring log