It’s a second job. They’re getting paid by the stadium or the 49ers, not the police dept, so not overtime.
A lot of places the city will contract with the team. So while the team pays for the police service, the officers are actually being paid by the city and it counts as overtime. The issue that arises is that pensions are based on what you make in your best year, so guys can really pad their pensions by working a bunch of OT. Where I live there was a cop who worked almost 1400 hour of OT in one year, and that’s on top of a $70 ,000 base. There are sergeants making nearly 200,000 a year.