Narrative:

Taxiing out on the b-south line a ground tug traveling from my right to left turned in front of the aircraft. I saw the tug and began to bring the aircraft to a stop. My first officer; who was initially heads down; looked up and without warning slammed the brakes on; bringing the aircraft to an abrupt stop. I set the parking brake and immediately called the flight attendants. They reported that all the passengers were seated with seat belts on and everyone was ok and there were no injuries. I then spoke to each flight attendant and asked if they were ok. The only flight attendant that had taken a fall said she had banged her knee but was not injured and wanted to continue the flight. The other flight attendant's had not fallen and each indicated that they were not injured and were ok to continue. I double checked with the flight attendant that had fallen to ensure she was not injured; she assured me she was not injured and wanted to continue. I did a brief PA to inform the passengers what had happened. I then spoke to the ramp control; they had witnessed the event and were going to review the tapes to determine the identification of the tug driver who cut us off. I then had a conversation with the first officer about control of the aircraft while in the taxi phase and the use of aircraft brakes. The flight continued normally to [destination]. I checked again with the fas after the flight and each one assured me that they were not injured.

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Original NASA ASRS Text

Title: B737 Captain reported the First Officer brought the aircraft to an abrupt stop in reaction to a potential collision with a tug during taxi at ORD.

Narrative: Taxiing out on the B-South line a ground tug traveling from my right to left turned in front of the aircraft. I saw the tug and began to bring the aircraft to a stop. My First Officer; who was initially heads down; looked up and without warning slammed the brakes on; bringing the aircraft to an abrupt stop. I set the parking brake and immediately called the flight attendants. They reported that all the passengers were seated with seat belts on and everyone was ok and there were no injuries. I then spoke to each flight attendant and asked if they were ok. The only flight attendant that had taken a fall said she had banged her knee but was not injured and wanted to continue the flight. The other FA's had not fallen and each indicated that they were not injured and were ok to continue. I double checked with the FA that had fallen to ensure she was not injured; she assured me she was not injured and wanted to continue. I did a brief PA to inform the passengers what had happened. I then spoke to the ramp control; they had witnessed the event and were going to review the tapes to determine the ID of the tug driver who cut us off. I then had a conversation with the F/O about control of the aircraft while in the taxi phase and the use of aircraft brakes. The flight continued normally to [destination]. I checked again with the FAs after the flight and each one assured me that they were not injured.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.