Authorities said he was walking when two cars approached him. One car avoided him but the other could not, authorities said.
"The driver called in the accident and waited at the scene," said Lt. Gary Strachan, a spokesman for the Orange County Sheriff's Department. "No one was arrested."
Strachan said deputies were investigating why Pasquale was in the street.
Pasquale made the first appearance of his college career in a 58-20 victory over Nevada on Aug. 31.
"This is a tragic loss," UCLA Coach Jim Mora said. "Nick was an outstanding young man who had a positive impact on everyone who knew him. He was a great teammate who was loved and respected by his entire team. Our thoughts are with the Pasquale family."
Pasquale had been a standout player at San Clemente High School and was one of the key players who helped the Tritons reach the Southern Section Pac-5 championship game in 2011.
Pasquale was named All-Orange County.
"We talk with our kids a lot about what it means to be Triton, being a close-knit community, that we're one town and one team," San Clemente Coach Jaime Ortiz said.
"Whenever I describe what we expect, I think of Nick. He was the epitome of what it meant to be a Triton, on and off the field. He was an undersized cornerback and not the fastest guy, but he always found a way to make things happen."
Pasquale earned a walk-on spot with the Bruins and spent last season as a member of the scout team.
"The UCLA family lost a wonderful young man who represented the university, his team and his family well," UCLA Athletic Director Dan Guerrero said. "Our hearts go out to the Pasquale family, and we will do everything we can to assist and support them, as well as his teammates, as they go through this unthinkable tragedy."