Actually, it’s the ongoing special protection detail that’s against 14th Amendment rules. The police are not supposed to provide more protection to one group of people than others.
Also, with many such jobs, the officers are working security off-duty as a side job with the permission of their departments. They are basically unionized private security guards at that point and they are perfectly free to walk en masse.
As for your first contention, there is a compelling state interest in having sporting events with huge audiences be conducted peaceably, so it’s a legitimate case for extra police protection, commensurate with the potential hazard of disorder.
If it’s off-duty moonlighting, that may be an out. It’s the owner who specifically wants police personnel as a deterrent, rather than mall cops and Pinkertons. But arguments can be made that the sheriffs, while off-duty, are using the prestige of their office to get this particular job. I don’t know if that’s relevant or not, though.