The Angels postponed Thursday night's game with Oakland and players planned to gather to remember their teammate, manager Mike Scioscia said.
"It is a tragedy that will never be forgotten," he said at an Angel Stadium news conference.
The 22-year-old Adenhart was a passenger in a silver Mitsubishi Eclipse that was broadsided in an intersection about 12:30 a.m. by a minivan that apparently ran a red light, police said.
The impact spun around both vehicles, and one then struck another car but that driver was not hurt, police said.
The minivan driver fled the crash scene on foot and was captured a half-hour later. Police identified him as Andrew Thomas Gallo, 22, of Riverside, and said he had a suspended license because of a previous drunken driving conviction.
Preliminary results indicated Gallo's blood-alcohol level was above the legal limit, police Lt. Kevin Hamilton said.
He could face charges including vehicular manslaughter or possibly murder, Hamilton said.
Adenhart died in surgery at the University of California, Irvine Medical Center. A 27-year-old man in the car and the driver, 20-year-old Courtney Frances Stewart of Diamond Bar, were pronounced dead at the scene, police said.
Stewart's mother said her daughter and Adenhart had known each other since last season but were not dating as far as she knew, Hamilton said.
The mother said Adenhart and the others had gone dancing at a club about a block away from the crash site, although the crash scene appeared to indicate the car was heading in the direction of the club, Hamilton said.
A 21-year-old passenger in the van was treated for minor injuries, police said.
Adenhart's death came shortly after he made his fourth major league start in Wednesday night's loss to Oakland. He threw six scoreless innings. Adenhart's father had flown out from Baltimore to watch the game.
"He summoned his father the day before and he said, 'You better come here because something special's gonna happen,'" said Adenhart's agent, Scott Boras.
After the game, "he was so elated...he felt like a major leaguer," Boras said, weeping.
Adenhart struggled with a 9.00 ERA in three starts with the Angels last season, but Scioscia said last month the pitcher had worked hard over the winter and arrived at spring training with a purpose.
Adenhart is survived by his parents, Jim and Janet.
"He lived his dream and was blessed to be part of an organization comprised of such warm, caring, and compassionate people," the family said in a statement issued through the team.
"The Angels were his extended family. Thanks to all of Nick's loyal supporters and fans throughout his career. He will always be in everyone's hearts forever."
The Major League Baseball Players Association said its members were shaken and saddened about the accident.
"Just hours before the accident, Nick demonstrated his passion for baseball and his prospects for a very bright future when he pitched six scoreless innings for the Angels," the association said in a statement.
Fans, some wearing Angels shirts or carrying flowers, gathered at the intersection where the accident occurred Thursday.
Adenhart, a Maryland native who starred at Williamsport (Md.) High School, began the season this week as the Angels' No. 3 starter because of injuries to John Lackey, Ervin Santana and Kelvim Escobar, all of whom are on the disabled list.
The pitcher made his major league debut May 1 of last year, also against Oakland. He made two other starts, getting his only decision in a victory over the Chicago White Sox on May 12. He was 37-28 in the minor leagues from 2005-08, including 9-13 last year at Triple-A Salt Lake.
Adenhart pitched for the Arkansas Travelers while in the minors.
Aaron Wells was Adenhart's athletic trainer in 2005 when he played for Utah's Orem Owlz, a rookie league affiliate with the Angels.
"It was very obvious that he was going to be a successful professional pitcher," said Wells, now the team's general manager. "Very humble, extremely good in the club house. He was just such an unassuming guy, just went out and did his business."
There was a moment of silence to remember Adenhart before several major league games Thursday.