It happened at Auto Center Drive and Orangethorpe Avenue, near the 5 Freeway.
Police say an off-duty officer was on his way to work when he witnessed a man and a woman arguing. When the officer tried to intervene, police say the man lunged at the officer and the officer opened fire.
The man then made a run for it but police later caught up with him. He was taken to the hospital with non-life-threatening injuries.
The woman was taken in for questioning.
