From what I saw, it first became an issue because the shots were outside but extremely close (3rd base line?) and for anyone near, it likely SOUNDED like live fire inside the park. In an effort to keep the panic inside to a minimum and keep people from trampling people, they showed on all the video screens that the shots were OUTSIDE the stadium and staying INSIDE the stadium for safety was the best plan.
Police responded, one of the persons involved in the shooting may have been a stadium employee, and the game was suspended and only after the scene was cleared were people exiting.
But perhaps I got that wrong. It is media reporting after all, and I wasn't there.
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!