RIO DE JANEIRO — In the dying sport of amateur boxing in America, where the increasing fear of brain injuries has deterred potential standouts from pursuing the sweet science, there is another major factor that could also continue to extinguish the passion.

Controversial scoring decisions.

Twenty-year old Gary Antuanne Russell walked away from a horde of media in disgust and bewilderment — understandably. He had just lost a split decision to Fazliddin Gaibnazarov of Uzbekistan in the light welterweight quarterfinals at Riocentro Pavilion 6 on Tuesday.

Russell was inconsolable because he essentially dominated the final two rounds of the three-round fight but lost by 1 point, a combined 76-75 on the judges’ scorecards.

USA boxing and their fighters fully realize that the unpredictability of officiating is nearly as big of a detractor in the sport as the opponent. They can train to chase gold, follow the strict guidelines for scoring points, and yet be snatched of victory by controversial judging.

It has discouraged some amateur boxers from delving into Olympic boxing, choosing instead to pursue professional careers.

In Russell’s situation, the controversial round was the second, where Gaibnazarov was warned by French referee Fathi Madfoua for being inactive. Russell was the aggressor, yet judge Roland Juhasz of Hungary and judge Kestutis Bagdanavicius of Lithuania each awarded Gaibnazarov the round by a 10-9 score. Italian judge Enrico Licini gave Russell the round.

Russell dominated the final round and won on all three judges’ cards, but it hardly mattered. Russell has worked arduously the past few years to reach this point, turning down a scholarship from the University of Maryland, qualifying in Baku, Azerbaijan, then winning his first two bouts in Rio before essentially having to knock out his opponent to win the fight.

“It’s just ridiculous to me,’’ US men’s associate coach Kay Koroma said. “I don’t think Gary lost any round. The kid [Gaibnazarov] was in retreat mode the whole time. He couldn’t get a punch off on Gary. Gary was catching him with the clean, harder shots. You couldn’t have a better fight. Gary was using his jab very well. He listened to everything we said. For them to stick him up like that was bad.’’

And now Koroma is left to explain to his fighter why the struggle is truly worth it.

“With a kid like him, he just feels like, ‘What am I in here for?’ ’’ Koroma said. “It just bothers me to see that.’’

Koroma and the rest of the United States staff go into every tournament realizing the possibility of a poor decision. Defending world amateur bantamweight champion Michael John Conlan of Ireland lost a disheartening unanimous decision to Russian Vladimir Nikitin when it appeared Conlan dominated the fight with Nikitin bleeding profusely from his left eye. Conlan was livid after the decision.

“They’re [expletive] cheats,’’ Conlan said on Irish television. “They’re known for being cheats. Amateur boxing stinks from the core right to the top. My dreams are shattered. I will never box again for AIBA [Amateur International Boxing Association].’’

Olympic boxing has a history of controversial officiating, most notably light middleweight Roy Jones Jr. losing a decision to Korean Park Si-hun in Seoul in 1988. After the fight, a battered Si-hun grabbed Jones’s arm and raised it to acknowledge the American’s performance.

Russell gathered himself enough to speak with the media, even being gracious enough to congratulate Gaibnazarov.

“I believe I pulled away, I believe I won,’’ he said. “[The Conlan fight] puts a little frustration on a lot of people’s mental [state], especially going into [my] fight and you’re trying to be comfortable. And seeing a fight go down and giving a unanimous decision [to Nikitin] knowing that [Conlan] won hands down, that kind of smokes you out mentally.

“Everybody that comes in there, I’m sure they believe slightly that the odds are against them.’’

What frustrated Team USA was the confounding scoring system. The AIBA stresses aggressiveness and activity. But it appears those skills are subjective. Gaibnazarov was warned several times for rough-housing tactics and once for inactivity, when he began dancing back and forth during the second round, yet two judges ruled he won that round.

“Anybody can be beaten here and the judging has been atrocious,’’ Team USA head coach Billy Walsh said. “The last time I saw it this bad was Seoul in 1988. This is the highest pinnacle of our sport. We’re supposed to have the best officials. I’d like to believe everybody is honest, you know? It’s a great game; all we gotta do is be honest.’’

Nikitin is the next opponent for the US’s Shakur Stevenson, who breezed past Erdenebat Tsendbaatar of Mongolia in a unanimous decision. Inasmuch as Stevenson, now guaranteed at least a bronze medal, will be prepared and likely the favorite against Nikitin, he has to prepare for the possibility that it could be taken away by bizarre officiating.

That’s a fact American boxers are dealing with, the distinct chance Olympic dreams can be dashed inexplicably. Shakur is among a dying breed; he has accepted amateur boxing with all its warts and has embraced it.

“I guess I gotta make it clear [that I’m winning the fight],’’ Stevenson said. “But I thought Conlan made it clear. But I guess the judges saw different.’’

Gary Washburn can be reached at gwashburn@globe.com. Follow him on Twitter @GwashburnGlobe.