According to the LA Times, eye witnesses told police a red minivan ran a red light, striking a silver Mitsubishi that was carrying Adenhart and three others.
Two people were reportedly pronounced dead at the scene by paramedics. The other two passengers were taken to a nearby hospital, where a third individual was later pronounced dead, Fullerton Police Lt. Craig Brower told the LA Times.
The driver of the minivan fled the scene of the accident on foot. However, was taken into custody shortly thereafter on suspicion of hit and run.
"The Angels family has suffered a tremendous loss today. We are deeply saddened and shocked by this tragic loss. Our thoughts and prayers go out to Nick's family, friends' loved ones and fans," General Manager Tony Reagins said in a statement on Thursday.
Adenhart's family, including parents Jim and Janet, also issued a statement on Thursday.
"He lived his dream and was blessed to be part of an organization comprised of such warm, caring, and compassionate people," the family's statement read. "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."
Adenhart, one of the Angels' top pitching prospects, took the mound on Wednesday night, pitching six shutout innings with five strikeouts against the Oakland A's in his first appearance of the new season.
The young pitcher made his major league debut on May 1 last season for the Angels. He pitched in three games in 2008 with a 1-0 record.
Related Content from AccessHollywood.com: