Two groups of young men — one largely Hispanic and another mostly white men with fraternity ties — clashed at a house party in the Oread neighborhood in February 2012, leading to the death of one man, and a charge of involuntary manslaughter against another.

That was the testimony Monday in the retrial of Justin P. Gonzalez, who is accused of hitting Nicholas Sardina over the head with a beer bottle and causing an injury that led to his death the next day.

The first trial ended in a mistrial in December 2013 when a jury could not reach a unanimous verdict.

What they all shared in common, according to testimony, was that they had all been drinking heavily the night of Feb. 25, and members of each group were friends with different women who shared a house at 301 W. 14th St. where the party and fight took place.

Cassidy Judy, who is now 23, said he didn’t particularly know either of the two groups at the party that night. He had come there to meet up with a friend and one of the roommates of the house who were not involved in the party. But he said it was immediately apparent that the difference between the groups was their ethnicity.

“They were not white,” Cassidy said of the first group, which already had a party underway when he arrived around midnight. “I don’t want to say Mexican. That’s a stereotype that I’m falling into.”

He described the second group, which arrived later, around 2 or 2:30 a.m., as “a frat group.”

The party mainly involved a tight-knit group of friends who’d grown up together in the Kansas City area and attended Bishop Miege High School. Whitney Beck, one of the women who lived at the house, helped organize the party with Gonzalez and several other friends, including Jake Anderson.

Anderson testified Monday that the party began around 10 p.m., although he had started drinking a few hours earlier. Some individuals brought six-packs of beer, but there was also a keg of beer on the back porch, as well as a table set up in the living room for playing a drinking contest known as “beer pong.”

Around 2 a.m., Anderson said, one of the other roommates came home with a group of other friends, including Sardina.

“They were dressed in a nice attire,” Anderson said. “I just thought they were frat boys.”

The other roommate became angry that the party was still going on and insisted the music be turned off and that everyone leave. From that point on, witnesses said, tensions between the two groups escalated.

But after more than two years since the incident occurred, many of the witnesses said they no longer remembered exactly what happened, or who instigated the fight, and prosecutors repeatedly had to show them transcripts of statements they had given police or testimony they’d given in previous hearings to refresh their memory.

Anderson said he remembered hearing some of the fraternity men make disrespectful comments about his friend, Whitney. He approached them and told them to stop making such comments.

Anderson also remembered shouting an obscene curse at the “frat boys.” Within seconds, according to witnesses, Sardina shoved Anderson into a wall. Anderson pushed back, but Sardina reportedly punched him hard across the left cheek.

Cassidy testified that he jumped into the melee in an effort to keep people apart but ended up taking several punches himself.

At one point, prosecutors allege, Gonzalez picked up a beer bottle and hit Sardina in the back of the head. At first, it didn’t appear Sardina had suffered a serious injury. He and other friends reportedly walked to a fraternity house in the 1600 block of Tennessee where they spent the night.

According to earlier testimony, Sardina had been drinking heavily and taking drugs before arriving at the party. He reportedly had taken at least two doses of a generic form of the anti-anxiety drug Xanax, and an autopsy showed signs of cocaine in his system after he died the next day.

Prosecutors say the cause of death was blunt trauma to the head.

The main question before the jury will be whether Gonzalez acted recklessly, or whether he acted with reasonable force in an effort to rescue his friend Anderson from the fight.

The trial is expected to continue at least through the rest of this week.