The Newhall incident involved CHP officers; the Onion Field incident involved LAPD officers who were kidnapped, one was killed.
At Newhall, two CHP officers (in one car) pulled up behind the suspects who had threatened a vehicle on the freeway. The driver got out his side next to one patrolman. The other patrolman went to the passenger side.The passenger opened his door and shot that patrolman. Then the driver shot the distracted patrolman right next to him.
When another CHP car showed up they were under fire immediately. The bad guys now had the officers' weapons. Those two patrolman didn't last long. A witness in the restaurant tried to help. He came out and grabbed an officer's .357 and opened fire--it wasn't fully loaded. One of his shot was the only one that hit a bad guy---who wasn't seriously wounded. With his gun empty, the smaritan fled.
One bad guy later invaded a home and took hostages--who weren't harmed. The other went to a trailor where an armed individual was threatened and persuaded to surrender his weapon and come out---he did. He was severely beaten with his own weapon. The bad guy either had no weapon, or it was empty.
One suspect ended up a suicide. The other went to prison.
In the Onion Field incident, an officer surrendered his weapon to the bad guys who had his partner at gun point. Then both LAPD officers were driven to an oinion field. One was executed, the other escaped.
Ayoob gave an excellent account of the Newhall incident in his book: The Ayoob Files: The Book.