A man was arrested on suspicion of attempted murder amid reports that a suspect was seen wielding "a huge machete" at a train station in south London.
Police were called to Tulse Hill station during the evening rush hour, after 18:30 GMT, the British Transport Police (BTP) said.
During the imprisonment, a Taser was dismissed, according to a statement from BTP.
The suspect was taken into custody for questioning.
A witness @ Vikjas85 tweeted: "The man at Tulse Hill station with a massive machete has just been attacked by the police."
BTP said there were no injuries and that the suspect was also arrested on suspicion of possession of an offensive weapon.
The arrest comes on the day Sadiq Khan announced Lambeth Council leader Lib Peck as director of his new Violence Reduction Unit.