Javeen Kudhil, the witness giving evidence at Birmingham Crown Court, told jurors how he and his friends ran from the house after victim Rezwan Ali collapsed in the kitchen.
Mr Ali, 19, suffered a cardiac arrest in the kitchen after he was knifed three times to the chest and arm, including a four-inch wound to the heart which severed a major artery.
Rajan Natt, 20, is accused of murdering Mr Ali during the fight, which unfolded between two groups at a house in Willows Road, in Walsall, on January 14, 2018.
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Mr Kudhil said a group of 10 or more people were involved in a fight.
He said: “The lads were outside, the girls weren’t, they remained in the kitchen.
"The fight just broke out and as it did it was a bit like a brawl, there was so much happening, so many people fighting.
"I was going back into the kitchen. Rezwan was walking past, he’s come in and turned to his left and walked straight down the kitchen.
"I’ve seen his body sway, he went straight onto the wall, smack, and dropped straight back.
“I was standing at the right shoulder of Rajan Natt, I don’t recall him walking into the kitchen.
“I saw the blood and said to my friend let’s get out of here.”
Mr Kudhil said people then started screaming “he’s been stabbed”.
The Crown alleges Natt fled with his friends, before getting a taxi, accusing him of later phoning another party guest in a bid to secure an “alibi” which could place him away from the stabbing.
Natt, of Castle Street, West Bromwich, denies any wrongdoing.
The trial continues.