Lee Rowley, 22, approached the victim from behind and forced the 17-year-old male to the ground.
He threatened the victim in Higher Kingston and made off with their wallet shortly after 7.30pm on Monday 7 November.
Officers tracked Rowley down and arrested him three days later in Glastonbury.
He pleaded guilty to one count of robbery and was jailed for three years at Taunton Crown Court on Friday 17 March.
He also admitted one count of possession of a bladed article relating to being found carrying a screwdriver in Glastonbury, one day before the robbery. He received a three-month sentence for that offence, to run consecutively.
The officer in the case, PC Jim Card, said: “This was a particularly unpleasant street robbery in Yeovil, which led to the victim attending hospital.
“Enquiries were quickly carried out to identify Lee Rowley as the offender and he was arrested a few days later in Glastonbury.
“We welcome the significant custodial sentence handed to him by the courts today and hope it acts as a reminder to people that the police and courts will look to deal robustly with dangerous offenders.”
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