That goes many different ways almost all are not good. I'll explain why:As prior military leo, I was trained always to pay attention to the back stop before taking a shot. Even in a crowd, most people will distance themselves from a shooter in a damn hurry once the first shot has been fired. I figure that by the time I've found and taken adequate cover, the crowd should have dispersed sufficiently for me to take proper aim and make an effective shot. I don't think I could live with the knowledge that I had the means to take action and failed to do so out of fear of harm to myself or legal consequences after the fact. As the quote goes, all evil requires to prevail is for good men to do nothing.
He stated it's a small park and there were up to 3,000+ people there . People will be running in all directions . You telling me you are going to take your eyes off the shooter and try to make your way through a large crowd to try and find cover? 1,000+ other people will have that same idea instead of finding an exit .
Not to mention how often do you go to such events alone? You planning on ditching your family to find this cover ? Say you take them with you to cover. You get a shot and boom you hit him! Then you discover he is wearing body armor . Now he will start firing directly at you and your family.
do you dress like a cop or wear tactical type clothing ? If not you waiting to make your move from your cover means there are now two gunmen in the park when the police do arrive . You could very easily be mistaken for the shooter .
I could go on and on about the pros and cons here. Bottom line is this :
If you can stop a threat safely then do it! If no clear shot can be had then you shouldn't hang around. Making a life or death choice with your heart instead of your brain can have disastrous consequences.