Date: 202009
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ramp ZZZ
Second aircraft: Regional Jet CL65; Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Situational Awareness; Confusion
Anomaly: Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure; Company Policy; Airport
Primary problem: Procedure

Narrative: I was serving as First Officer. Enroute; the Captain was the Pilot Flying and I was the Pilot Monitoring. Upon exiting the runway; the Tower Controller gave us the taxi instructions 'high-speed; ...; cross XX center' and while on the taxiway; the Tower handed us over to Ground.Before reaching the next taxiway; the Ground Controller instructed us to follow an aircraft under tow which we did on a route until the under-tow continued straight and we were instructed to turn right. The Ground Controller requested 'tell me how the Ramp is going to bring you in' and I contacted Ramp as we were making the turn. The Ramp Controller instructed us to the gate and I relayed that information to the Ground Controller. He acknowledged that information and the Ground Controller had nothing else to say.Continuing on the taxiway; the Captain continued and then proceeded to turn left to enter the alley as instructed. There was an outbound aircraft occupying the West line of alley. As the Captain completed the turn; and with the nose of our aircraft pointed north; he and I both saw another aircraft accelerate from behind us; over our left shoulders; and proceed northeasterly; diagonally; to maneuver towards the East line. This other Captain aimed his aircraft between the aircraft occupying the west line and us. The Captain applied firm brake pressure and our aircraft responded and stopped. Once the conflicting aircraft passed us we could see their registration; and we proceeded to follow this flight north along the east side of the alley. They taxied to their gate; once he was clear to the left we continued to our gate. No further communication was received from the Ramp Controller during our taxi; and we heard nothing on either ground or Ramp frequency noting that there might be a potential conflict between us and the other aircraft.While there was no contact between our aircraft; or between the other aircraft had the Captain not taken the action he did then wing-to-wing contact between us and them would have occurred.  The maneuver by the other aircraft was very much unsafe; definitely unprofessional; and against the flow of the taxiway.




Synopsis: Air carrier pilot reported they had to brake to avoid collision with another taxiing aircraft which cut them off overtaking them from a diagonal taxiway.