The Scotsman has learned of the Good Friday assault after revealing last week a ticket examiner had been left traumatised trying to eject brawling teenagers from another ScotRail service.
The victims in the latest incident to come to light were members of the train operator’s “travel safe team”, which was established in October to “quickly focus on emerging hot spots”.
British Transport Police (BTP) confirmed: “Officers received a report of a rail staff assault on board a train between Paisley Gilmour Street and Hillington East stations just after 10pm on April 15.
“Three members of rail staff and a man suffered minor injuries as a result of the assault.
“No arrests have been made at this time and enquiries are ongoing.”
The BTP spokesperson said one of those injured was treated in hospital and released the following day.
The Rail, Maritime and Transport union has said staff would boycott routes plagued by anti-social behaviour unless more action is taken.
Scottish organiser Mick Hogg said: “The travel safe team was challenged and assaulted.
"They are not the answer. We welcome more jobs, but travel teams are not there to deal with anti-social behaviour.
"We need more BTP visual at stations and on trains."
Mr Hogg said staff assaults were “continuous” on some ScotRail routes.
He said: “It will no longer be tolerated staff being assaulted.”
Assaults on rail staff in Scotland increased by 11 per cent to 72 between April and December last year, compared to 65 in the same period in 2019, BTP figures published by the Scottish Railways Policing Committee showed.
BTP said: “We have increased our high visibility patrols in Scotland following anti-social behaviour on trains.”
ScotRail said the attack on its travel safe team was not related to incidents of youth anti-social behaviour in West Dunbartonshire, such as the one encountered by a ticket examiner on the Balloch-Glasgow line on May 1.
She single-handedly bundled a gang of teenagers off the train after they attacked a younger boy with a bottle.
Transport minister Jenny Gilruth told MSPs in February that members of the travel safe team “bring with them a wealth of experience working from frontline customer-facing roles”.
She said: “This is the sort of public-facing initiative that we should be encouraging because we know that when staff are deployed in teams, even just a presence can act as a deterrent, helping keep the public safe.”
ScotRail said: "The team was designed to be a reactive resource with the ability to quickly focus on emerging hot spots.
"They actively engage and educate individuals and groups on the impact of unsafe behaviours when on or around the railway environment.
"We have seen a drop in reported events during and after the anti-social behaviour exercises.”
ScotRail security and crime manager Stephen Elliot said: “The safety of our customers and employees is our number one priority.
“Anti-social behaviour, whether that’s physical violence, verbal abuse or any other form, is completely unacceptable.
“Everyone has the right to go about their day in peace, so we’ll continue to work with the authorities to ensure anyone responsible for anti-social behaviour is brought to justice.”