Police were called to the scene of an accident at 8:33 a.m., police Officer Albie Esparza said.
Officers found a bicyclist had struck a woman in her 40s who was crossing in the crosswalk, causing a life-threatening head injury. Preliminary information suggests the woman was crossing legally with the light, Esparza said.
The bicyclist remained at the scene and was being interviewed by investigators.
Esparza said the bicyclist would face the same potential legal repercussions as the driver of any car involved in a collision with a pedestrian, if they were found to be at fault.
"Every bicyclist in the city should be reminded each and every day that all the laws on the books apply to them too," Esparza said. "They need to stop at every stop sign and every stop light."