The man was arrested shortly before 9pm on Friday in St Christopher Street, Lavender Hill, police spokesman Captain FC van Wyk said.
Vigilant police officers saw two men riding on a Moto Mia motorcycle.
When they saw the cops they tried to speed off.
Officers gave chase and the suspects lost control of the bike and fell. The rider ran away.
“The one suspect was caught and upon searching him, members found a Luger M80 parabellum 9mm [pistol], with no serial number, and 13 live rounds of ammunition in his pants,” he says.
The 21-year-old suspect was arrested.
Once charged, he would appear in the Wynberg Magistrates’ Court for possession of an unlicensed and prohibited firearm and ammunition.