Police pulled a Taser on a man carrying a claw hammer on a Tube train at South Kensington station.
Officers were called to the station on Pelham Street just after 2.30pm on Tuesday (August 23) after receiving calls that a member of staff had been punched and assaulted.
The suspect then vandalised a station toilet before heading to the platforms to board a train.
When British Transport Police (BTP) officers boarded the train to speak to the man they saw he was carrying the weapon.
Despite several warnings he refused to drop the hammer, forcing police to draw the Taser.
However, the weapon was eventually dropped without police having to fire the electroshock gun.
A 19-year-old from Thornton Heath was arrested on suspicion of common assault, possession of an offensive weapon and assaulting a police officer, and released on bail until October 12.
The use of Tasers has been called into question in recent weeks following the death of former Aston Villa stricker Dalian Atkinson, who died shortly after one was used on him by police in Telford.
Anyone who can help BTP with their inquiries can text 61016 or call 0800 40 50 40 quoting reference 283 of 23/08/2016.
Last year an Underground worker was assaulted following a row over tickets , and the year before that a member of staff was attacked at Park Royal Tube station .