Police spokesman Johan Rheeder told reporters that the victim had tried to disarm a policeman during a post-match pitch invasion and the gun went off accidentally.
"A man tried to take the gun of a police officer and it went off during the scuffle, fatally wounding him," Rheeder said.
Spectators invaded the Nelson Mandela Bay Stadium pitch in the port city to celebrate Kaizer Chiefs winning the South African Premiership title.
Although the Soweto club clinched first place 17 days ago, it was presented with the trophy only after a 2-0 final-round victory over host Chippa United.
The match attracted a sell-out 45,000 crowd to a stadium built for the 2010 FIFA World Cup.
