Hayes, 29, is claiming self-defense.
During his nearly two-hour testimony Saturday, Hayes painted a picture of Smith, 34, as an angry, aggressive and possibly drunk attacker who was about to kill Hayes before Hayes shot Smith eight times, including seven times in the back.
"I didn't want to kill Will Smith. I didn't want to kill nobody," said Hayes, who insisted he didn't begin firing at Smith until he saw a "black weapon" in Smith's hand and heard a "pop."
Hayes was the only witness to place a gun in Smith's hand that night. Police say a loaded gun was found in Smith's SUV. Prosecutors say it was never fired that night and that Smith never grabbed it.
Hayes also testified that he did not shoot Smith's wife, Racquel, who was hit once through both of her legs before Will Smith was shot. Hayes said he did not know who shot Racquel, who he said was attempting to hold her husband back and yelling something to the effect of "No, baby, no" as Smith reached into his vehicle to retrieve a gun.
Hayes insisted he feared for his life after Smith addressed him with a racial epithet and told him, "... you got your gun. Well, I'm going to get mine, and I'll show you what to do with it."
"What else could I think? I think he's gonna show me what to do with it. I think he's about to kill me," said Hayes, who said Smith threw a cup containing some type of alcohol at him and repeatedly punched him in the face before threatening to grab his gun. "I knew I was gonna be shot. I probably would've died. I knew for a fact I was gonna get shot."
Hayes also testified that his .45-caliber handgun fired several times rapidly and that he didn't expect it to go off that many times and tried to stop it.
Asked why he didn't turn and run, Hayes said he wasn't going to leave his friend Kevin O'Neal behind and that he was sure he would have been shot while trying to flee.
The prosecution, meanwhile, spent most of the day poking holes in Hayes' claims, including pointing out that no other witnesses, including O'Neal, saw Smith retreat into his vehicle, heard Smith threaten to get his own gun or saw Smith hit Hayes.
Prosecutors pointed out that Hayes never told investigators that he saw a gun in Smith's hands that night, nor did he mention that detail in two conversations he had that were recorded on the scene immediately following the shooting. Hayes repeatedly replied that he "never gave a full statement to anyone."
Prosecutors also called a rebuttal witness, a firearms expert who said there was no evidence that Smith had fired a gun when he died.
According to the prosecution, Hayes' claims about where he was standing when he shot Smith didn't match ballistic evidence or account for how a shell casing wound up inside Smith's vehicle.
Hayes said he couldn't account for what others saw and heard, but he insisted he was telling the truth.
The defense has hinted that someone might have removed evidence from the crime scene. Earlier this year, defense attorney John Fuller said a witness claimed to see Smith's friend and former New Orleans police captain Billy Ceravolo reach into the car. But those claims were proven false, as Ceravolo was not yet on the scene at the time the witness claimed to have seen him.
The fatal confrontation began that night after a pair of traffic incidents. The first happened when Smith appeared to bump Hayes, then drive away; the second occurred when Hayes crashed into Smith's Mercedes SUV after pursuing him a couple blocks away.
Hayes insisted the crash was accidental -- that he was looking down to unlock his phone and call 911 while O'Neal was trying to get Smith's license plate number. An expert testified Sunday that the crash appeared to be intentional.
Hayes said that following the collision, he was immediately rushed by a "Spanish guy" who was a passenger in Smith's SUV, later identified as Richard Hernandez. Multiple witnesses have testified to Hernandez's being the most aggressive person on the scene, removing his shirt and acting "ridiculous."
Hayes testified that he saw Hernandez remove a shiny object from his pocket -- possibly a knife -- and wrap it in his shirt before Hayes decided to retrieve his gun from the car. Hayes said Hernandez was the first one to yell out that Hayes had a gun, but he would be afraid to use it.
Hayes later testified that Hernandez ran away with his wife "way before" shots were fired.
Saints coach Sean Payton made his first appearance in court Saturday and sat next to Racquel for part of the morning. Payton had offered Smith a job as a coaching intern this summer, before he was killed.
Payton left in the middle of the proceedings to catch the team flight to Tampa. It's possible the Saints could be on the field against the Buccaneers on Sunday afternoon when the verdict is reached. Closing arguments are scheduled to begin at 10 a.m. ET.
Hayes, who played semi-pro football and played on the defensive line like Smith, said he did not know he had killed Smith until later that night, when he was in jail. But when asked Saturday if he was familiar with Smith, Hayes replied, "Yes, I really was. Not personally, but I knew him as a good football player." Hayes said he tried to incorporate some of Smith's game into his own.
Hayes appeared comfortable and focused throughout most of his testimony, directing many of his answers to the jury. He got choked up multiple times, especially when talking about his 6-year-old son, Cardell Jr.
Information from The Associated Press was included in this report.