Santa Clara built the San Tomas Aquino Creek trail for the health and enjoyment of the community before the stadium was ever built, which should give trail users some claim to access during stadium events.
However, it cannot now be opened during events because, as the editorial rightly points out, this could lead to terrorist incidents everybody would regret. Yet stadium safety might have been ensured without hijacking trail use. If the trail had been lowered to the creek bottom while passing the stadium and had been routed under the bridges leading into the stadium instead of becoming access to those bridges, and if it had been enclosed by a cage similar to those on bicycle bridge overpasses, the safety and convenience of neither trail nor stadium users would have been compromised, and little or nothing would have been added to stadium costs.
This could still be done.