Teenagers Benjamin Jeffcock and Dean Hartley were wandering through Hillsborough after downing at least eight pints when, for no reason, they set upon a man and two women on their way home.
When a "Good Samaritan" came to help, the pair attacked him too, prosecutor Liz Martin told Sheffield Crown Court.
Sending both youths to a young offenders' institution, Judge Alan Goldsack QC told them: "Your case is a classic illustration of one of the evils in our society at present - binge drinking leading to gratuitous violence on the streets of our city late at night.
"It is behaviour like yours which leads to decent people no longer going into their cities at night."
The victims, all in their mid-20s, had enjoyed a night out in The Hillsborough Hotel on Langsett Road and were waiting for a tram when they were attacked in August this year.
The two yobs attacked the man, knocking him unconscious. When the two women, aged 23 and 26, tried to pull the assailants off, Jeffcock, from Windsor Rise, Aston, turned on them. Hartley stamped on the injured man's head while his accomplice punched and ordered one of the women to hand over cash and her mobile.
The other woman fled to get help at the pub but was stopped by Jeffcock, an apprentice electrician. He threatened to use a knife as he robbed both the women of cash.
When a passer-by stopped to intervene Hartley, 19, called for 18-year-old Jeffcock to come and help attack him as well.
The injured victims needed hospital treatment, both women are now anxious about going out at night, and one later suffered flashbacks and nosebleeds.
Hartley, of Trafalgar Road, Wadsley, who had also swallowed an Ecstasy tablet, was arrested, and a bank card taken from one of the women was discovered on Jeffcock.
Jeffcock admitted two counts of robbery and two counts of causing actual bodily harm and was sentenced to a total of three years and six months.
Hartley admitted two counts of causing actual bodily harm, and was given three years with another four months for a separate assault.